Effects of heat treatment on microstructure and properties of Fe-based amorphous composite coatings

Abstract

It is found that heat treatment can improve the microstructure and properties of the coating. In this paper, the Fe-Cr-Mo-B-C amorphous composite coatings fabricated by laser cladding technology were heat treated at different temperatures. The effects of heat treatment temperature on the crystallisation, porosity, microhardness, and corrosion resistance of coatings were investigated. The experimental results show that the amorphous content and porosity after heat treatment, the comprehensive properties are improved, and the coating defects are solved. Both the amorphous content and the porosity affect the corrosion resistance of the coatings. The smaller the porosity, the higher the amorphous content, and the stronger the corrosion resistance of the coating. When the difference in amorphous content is small, the porosity of the coating becomes the dominant factor affecting the corrosion resistance of the coating. The experimental results shows that the best optimum heat treatment temperature for the coatings is 200°C.

Keywords

Fe-based amorphous composite coating heat treatment amorphous content porosity corrosion resistance

Introduction

Due to the unique structure of amorphous without the defects of traditional crystalline materials [1], Fe-based amorphous coatings have ultra-high strength, hardness, corrosion resistance, and wear resistance [2] and are easy to process [3]. Fe-based amorphous coatings have broad application potential in petrochemical, aerospace, shipbuilding, surgical tools, and biomedical implants [4]. In this regard, various coating techniques are used to deposit coating materials on the surface of the substrate to enhance its application [5]. There are many processes for preparing Fe-based amorphous coatings, including high-velocity oxygen fuel (HVOF) [6], arc spraying (AS) [7], detonation spraying (DS) [8], laser cladding (LC) [9], chemical vapour deposition (CVD) [10], etc. Among them, laser cladding technology has many advantages such as a fast cooling rate (up to 106 K/s), easy metallurgical bonding, a high degree of automation, strong environmental protection, small substrate deformation, and small heat-affected zone [11]. The so-called laser cladding refers to adding cladding materials on the surface of the substrate in a certain way (preset, powder addition, etc.). The high-energy laser beam is used to melt and rapidly solidify the substrate surface and the cladding material at the same time to obtain a coating that is tightly bonded to the substrate surface, which can effectively improve the wear resistance, corrosion resistance, and oxidation resistance of the substrate surface [12]. Fe-based amorphous coatings have been practically applied in manufacturing and remanufacturing fields [13]. Zhu et al. [14] laser cladded Fe-Ni-Si-B-V amorphous nanocrystalline composite coating on AISI 1045 steel substrate. The experimental results showed that the coating was composed of amorphous and a small amount of nanocrystalline. When the laser power was appropriately increased, the amorphous content in the coating increased. When the laser power and scanning speed were 4.8 kW and 3500 mm/min, respectively, the amorphous content in the coating reached the highest. Wu et al. [15] successfully prepared a Fe-based amorphous coating on the surface of steel by laser cladding technology. The maximum thickness of the coating was 1.2 mm, and the concept of a supercooled liquid region was first proposed.

However, amorphous coatings often have a severe problem, just pores, which can form channels for corrosive media to penetrate the coating, reducing the corrosion resistance of the coatings [16]. The methods to reduce the porosity of coatings mainly include sealing treatment [17], laser remelting [18], heat treatment [19], etc. Among them, heat treatment is the most common and economical process to improve the materials. Heat treatment is a process in that solid materials are heated, kept warm, and cooled to obtain expected properties by changing the structure of the materials. Heat treatment can process not only metallic materials [20], but also non-metallic materials [21], and even biological materials [22].

There are many literature reports on the heat treatment of Fe-based amorphous coatings. Chen et al. [23] conducted heat treatment on Ni-Cu-P amorphous coatings prepared by electroless plating. After the heat treatment, the metastable Ni₅P₄, Ni₁₂P₅, and Ni₅P₂ phases were transformed into stable Ni₃P phases, and Cu atoms were precipitated in the form of Ni(Cu) solid solution. The mechanical properties such as hardness, elastic modulus, and wear resistance of Ni-Cu-P coatings were affected by the microstructural evolution during crystallisation. Huang et al. [24] prepared Fe-based amorphous coatings by high-velocity air–fuel (HVAF) spraying process and studied the effect of vacuum heat treatment (VHT) on the erosion properties of coatings under the impact of alkaline sand-containing NaCl slurry. The coating after heat treatment had high hardness and good wear resistance, but the grains grew and the grain boundaries increased, leading to the increase of channels for chloride ions to enter the coating and the deterioration of erosion resistance. Zheng et al. [25] heat-treated amorphous coatings at different temperatures. After heat treatment, crystalline phases appeared in the coating with a more dense structure, while the hardness and erosion resistance were improved. However, coatings heat treated at 750°C exhibited the worst cavitation resistance due to decreased corrosion resistance. Our research group [26] used HVOF technology to fabricate Fe-based amorphous coatings on 304 stainless steel and studied the properties of the coatings after heat treatment at 150 and 250°C. The experimental results showed that the coating retained an utterly amorphous structure after heat treatment, and the porosity was reduced. With the increase in the temperature of heat treatment, the wear resistance, and corrosion resistance of the coatings in artificial seawater were improved, and the coatings had good creep resistance.

After heat treatment, the microstructure and interfacial bonding between the coating and the substrate is significantly improved, and the pores and cracks of the coating are reduced, thereby improving the performance of the coating. However, if the temperature is too high, the amorphous coating will crystallise, and the inherent properties of amorphous will gradually weaken or even disappear, causing changes in the coating performance. Amorphous content is also an essential factor affecting the corrosion resistance of Fe-based amorphous composite coatings. The lower the amorphous content, the worse the corrosion resistance of the coating [27]. In order to study the separate effects of amorphous content and porosity on the corrosion performance of amorphous coatings, Nayak et al. [28] prepared Fe-based amorphous composite coatings with the same amorphous content but different porosity and non-porous Fe-based amorphous ribbons with different amorphous content. The result showed that the corrosion behaviour of the coatings was mainly manifested in the local corrosion of porous amorphous/nanocrystalline regions and degradation of the passivation film at the amorphous/nanocrystalline interface. Therefore, they believed that when both the amorphous content and the porosity affected the corrosion resistance of the coating, the reduction of the amorphous content was the main factor.

In this paper, the Fe-Cr-Mo-B-C amorphous composite coatings fabricated by laser cladding were heat treated with different heat treatment temperatures, and the microstructure and properties before and after heat treatment were studied. In addition, the influence mechanism of heat treatment temperature on the microstructure and properties of the coatings was also investigated. It is found that heat treatment at an appropriate temperature can effectively reduce the porosity of Fe-based amorphous composite coating, improve its comprehensive properties, and effectively solve the defects of the original coating. This study will make a significant contribution to exploring the effects of amorphous content and porosity on corrosion resistance. The results show that the porosity of the coating becomes the dominant factor affecting the corrosion resistance of the coating when the difference in amorphous content is small.

Experiment

Process parameters

In this experiment, 45 steel was selected as the substrate material and Fe-based alloy powder (25.0–27.0 wt% Cr, 16.0–18.0 wt% Mo, 2.0–2.5 wt% C, 2.0–2.2 wt% B, and the balance Fe) with the particle size of 16–54 µm manufactured by Guangzhou Wandun Amorphous Trade Co., Ltd. was selected as the powder material. The Fe-based amorphous composite coating was prepared on the surface of 45 steel by laser cladding technology with laser power of 1400 and 1600 W, and lapping rate of 30% and 40% scanning speed of 10 mm/s, and the samples of 1#, 2#, and 3# are obtained, as shown in Table 1. Then, the heat treatment was performed at 150, 200, and 250°C for 30 min. The microstructure and properties of the coating before and after the heat treatment were compared, and the change mechanism was analysed. The cladding equipment was a 4 kW pulsed fibre laser (YLR-4000-S4, IPG, Germany) equipped with KUKA 6-axis robot (KR30HA). The laser spot was circular with diameter of 3 mm, and the protective gas was Ar with gas flow rate of 15 L/min. According to the previous DSC experimental results of our group [26], the glass transition temperature (T _g) of the Fe-based amorphous coating with this composition was 251.85 °C, and the crystallisation temperature (T _x) was 301.85°C, so the heat treatment temperature was set to below Tg of 150, 200, and 250°C. A muffle furnace (KSL-1700X-A2) was used as the equipment for heat treatment, and process parameters have been shown in Table 2.

Table 1

Process parameters of laser cladding.

Laser power (W)	Scanning speed (mm/s)	Overlap rate (%)	No. (#)
1400	10	30	1
1600	10	30	2
1400	10	40	3

Table 2

Process parameters of heat treatment.

Original coating (#)	Temperature (°C)	Time (min)	New no. (#)
1	150	30	1-1
1	200	30	1-2
1	250	30	1-3
2	150	30	2-1
2	200	30	2-2
2	250	30	2-3
3	150	30	3-1
3	200	30	3-2
3	250	30	3-3

Microstructure and performance

The heat-treated coatings were cut into samples of 5 mm × 5 mm × 10 mm using a wire cutting machine, and the surfaces of the samples were polished with 400, 800, 1500, and 3000 mesh sandpaper in turn, then were cleaned with ultrasonic. X-ray diffraction (XRD, D/max-2400, Cu K_α, Japan) was used to analyse the phase of the samples, and Jade software was used to analyse the crystalline composition and amorphous content. Laser scanning microscope (Zeiss LSM 800, Germany) was used to observe the cross-sectional morphology of the coatings, and Image J software was used to analyse the porosity of the coatings. The grain distribution of the samples after being immersed in aqua regia for 10 s was observed by scanning electron microscope (SEM, FEI Quanta 450 FEG, USA). The HV-1000 Vickers microhardness tester was used to test every 0.1 mm from the coating to the substrate on the side of the samples. The electrochemical corrosion test of the coating was carried out by CHI660E electrochemical workstation. The reference electrode for the test is a saturated calomel electrode and the comparison electrode is a platinum electrode. Before the test, the samples were cut into 5 mm × 5 mm × 2 mm, adhered to the copper sheet with conductive tape, and the non-test surface was sealed with epoxy resin. To obtain accurate electrochemical test results, the samples were immersed in the corrosion solution for 1800 s until the open circuit potential (OCP) stabilised. In the polarisation curve test, the scanning rate was 0.01 V/s and the prospect was −0.8 V to 0.4 V. During the electrochemical impedance spectroscopy (EIS) test, the frequency was 10⁻²∼10⁵ Hz. The impedance spectrum data were fitted using Z-View software to obtain Nyquist plots and Bode plots, as well as the parameters of each element of the EIS equivalent circuit. The corrosion solution for electrochemical tests was 3.5 wt.% NaCl solution. After the electrochemical experiment, the corrosion morphology of the coatings was observed by SEM.

Results and discussion

Structure and amorphous content

The XRD patterns and amorphous content of the coating after heat treatment are shown in Figure 1. Figure 1(a) suggests that the coating 1-1#, 1-2#, 1-3#, and the coating 1# have the same diffraction peak positions and they all have three crystal phases of B₆Fe₂₃, Fe-Cr, and Cr₂B. The diffraction peak intensity of the coating 1-3# is more robust, while the diffraction peak intensity of the coating 1-1# is weaker. With the increase of laser power, the diffraction peak intensity increases, and the amorphous content decreases, as shown in Figure 1(b). This phenomenon is caused by the diffusion of heat outside the molten pool, which will form the heat affected zone (HAZ). The higher the laser power is, the more heat will be absorbed by the coating, and the larger the HAZ will be formed. The cooling rate in HAZ is lower than the critical cooling rate required for the formation of amorphous, resulting in crystallisation of the coating [29]. From Figure 1(b) and Figure 1(c), it can be observed that the crystallisation law of the coating 2# and 3# after heat treatment is basically the same as that of the coating 1#. The diffraction peak intensity of the coating 2-3# and 3-3# is stronger, while the diffraction peak intensity of the coating 2-1# and 3-1# is weaker. In summary, it can be seen from the XRD pattern that as the heat treatment temperature increases, the diffraction peak of the coating tends to narrow but its shape remains basically the same, indicating that crystalline phases precipitate, and the crystalline phases are mainly B6F23, Fe-Cr, and Cr2B. In the range of 2θ = 70°–80°, the diffraction peak increases, showing the Cr2B phase increases. In the range of 2θ = 35°–45°, there are similar changes, indicating that the B6Fe23 phase increases. As shown in Figure 1(d), the amorphous content of the coating 1-3#, 2-3#, and 3-3# is significantly lower than that before heat treatment because of their higher temperature of heat treatment. During heat treatment, the closer the temperature is to the crystallisation temperature, the more heat the coating absorbs, and the more severe the crystallisation of the coating. The amorphous content of coating 1-2#, 2-2#, and 3-2# is also slightly lower than that before heat treatment, while there is almost no change for the amorphous content of coating 1-1#, 2-1#, and 3-1# because their heat treatment temperature is only 150°C. The lower the heat treatment temperature, the less heat the coating absorbs and the less likely the coating is to crystallise. The amorphous content of the Fe-based amorphous composite coatings can be maintained by a heat treatment process with a temperature of 150°C and a time of 30 min.

Cross-sectional morphology

Since the coating 1-3#, 2-3#, and 3-3# had relatively low amorphous content, the coating 1-3#, 2-3#, and 3-3# were excluded from subsequent experiments. Figure 2 exhbits the cross-sectional morphology of the coatings before and after heat treatment. It can be seen that there are many pores in the coatings before heat treatment. In the process of laser cladding, the gas at the bottom of the molten pool is difficult to discharge, thus pores formed. In addition, more holes are observed in coating # 2. The increase in laser power and temperature makes the liquid flow in the molten pool more intense, and the liquid splashing produced would lead to the formation of holes. After heat treatment, the coatings are tightly bonded to the substrate without cracks, with few pores, and the structure is denser than before heat treatment. Figure 3 shows the porosity of the coatings before and after heat treatment. When the temperature is 200°C (Figure 2(c,f,i)), the porosity of the coatings generally decreases, and the porosity of 0.387% for the coating 4-5# is the lowest. When the temperature is 150°C (Figure 2(b,e,h)), the porosity of 0.567% for the coating 3-1# is the lowest. Compared with coatings with different heat treatment temperatures, when the temperature is 200°C, the cross-sectional pores of the coatings are the least and the surface quality is the best. The reason is that the amorphous states of the coatings undergo structural relaxation, and the disordered atoms are rearranged into order, which makes some pores in the coating submerged, therefore the porosity of the coatings decreases and the density increases [30,31]. In addition, the self-melting reaction of Fe-based alloys occurs during heat treatment, which has a strong effect on the compactness of the coatings [32]. In general, the heat treatment process can reduce the porosity of Fe-based amorphous composite coatings and improve the surface quality of the coatings.

Microstructure

Figure 4 shows the microstructure of the coatings after heat treatment, compared with the coatings before heat treatment. The grains of the coatings are significantly increased after the heat treatment (as shown by the black particles in Figure 4), and some amorphous regions are also retained (as shown by the grey part in Figure 4). By comparing coatings with different temperatures of heat treatment, it can be observed that when the temperature is low, the coating hardly crystallises. The higher the temperature, the more heat the coatings absorb and the more grains appear, which is consisitent with the XRD experimental result. Finally, all coatings are dense without cracks, indicating that low-temperature heat treatment can maintain the surface quality of the coatings.

Microhardness

To evaluate the hardness of the coatings after heat treatment, microhardness tests were performed every 0.1 mm in the direction from the coating to the substrate on the cross-section of each sample. Figure 5 illustrates the microhardness of the coating 1#, 2#, and 3# after heat treatment, and the inset shows the morphology of the indentation, revealing a typical Vickers hardness indentation. From Figure 5(a) and Figure 5(b), it can be found that there are almost no obvious changes in the microhardness for coating 1# and coating 2# after heat treatment, indicating that the coatings after heat treatment maintain the characteristics of the original coatings. The coating was divided into coating area, diffusion area, and substrate, among which the microhardness of the coating area is the highest. Different from the above two coatings, as shown in Figure 5(c), the microhardness of the coating 3# after heat treatment is significantly improved, especially for the coating 3-2#. It can be found from Figure 5(d) more intuitively that there are no significant changes in the maximum microhardness and the average microhardness of the coating 1# and 2# after heat treatment, while that of the coating 3# has obviously improved. The maximum microhardness and the average microhardness of coating 3-2# reaches 1203.64 and 1084.18 HV respectively, compared with that of 1063.19 and 1008.25 HV for coating 3#, which may be due to the fact that the coating 3# has been generated more B₆Fe₂₃ and Cr₂B hard phases during heat treatment. The microhardness of the coating is not only determined by the amorphous content, but also related to the hard phase [33]. In general, the increase in hardness is always closely related to the special microstructure or phase composition of the material [34], which suggests that the microhardness of the coating is determined by the amorphous content and the hard phase composition.

Electrochemical corrosion properties

Since amorphous alloys have no grain boundaries, dislocations, and stacking faults, and the greater reactivity of the amorphous structure, which results in a greater presence of Cr ions in the passive film and also results in a more homogeneous distribution of Cr and Mo in the passive film, amorphous alloys have better corrosion resistance than crystals [35,36]. In order to compare the corrosion resistance changes of the coatings before and after heat treatment, electrochemical corrosion tests were performed in 3.5 wt.% NaCl solution. The OCP is measured for 30 min to ensure that the OCP becomes stable, so the electrochemical data measured later will be more accurate. From Figure 6(a), it can be discovered that the OCP of all coatings have reached a stable state before 30 min. Figure 6(b) is the Tafel polarisation curves of the coatings before and after heat treatment, the relevant parameters are determined using the Tafel extrapolation method [37], as shown in Table 3. In general, high corrosion potential (E _corr) and low corrosion current density (I _corr) indicate that the material has higher chemical stability and lower corrosion tendency [38,39]. It can be seen that the E _corr of all coatings after heat treatment slightly increases, and the I _corr decreases. Moreover, with the increase of heat treatment temperature, the porosity of the coating decreases, the current density decreases, and the corrosion resistance increases. Among them, the E _corr of −229 mV for the coating 1-2# is the highest, and the I _corr of 8.537 × 10⁻⁷ A/cm² is the lowest. However, the E _corr of −290 mV for the coating 2-1# is the lowest, and the I _corr of 3.732 × 10⁻⁶ A/cm² is the highest. Because the corrosion resistance of Fe-based amorphous coatings is jointly determined by the amorphous content and porosity, the higher the amorphous content, the lower the porosity, and the better the corrosion resistance of the coatings [16]. In order to resist the corrosion of Cl⁻, a passivation film is formed on the surface of the amorphous alloy, which consumes Cr element. The existence of pores provides a corrosion channel for Cl⁻, which makes a large number of Cl⁻ enter, so the Cr element is completely consumed, and Cr-depleted zones are formed [40]. Therefore, the corrosion performance reduces. Although the existence of Cr in the coating can effectively promote the formation of passive film and improve its corrosion resistance, the corrosion potential at the bottom of pores in the coating is higher than that at the outer surface of pores. This phenomenon will form a corrosion micro-cell with a large cathode and a small anode and dissolve the metal surface in the pores with a large anode current density. Then, the shape of the pores has a sudden change, and the surface free energy is high, which is easy to cause the fracture of the passivation film on the coating surface and accelerates the pore corrosion. Qin et al. [41] have believed that when the porosity of the coating is lower than 1.21%, its corrosion resistance is determined by the amorphous content. When the coating porosity is higher than 1.21%, its corrosion resistance is determined by the porosity. However, according to the experimental results in this paper, the above conclusions are not absolutely reliable. The difference in the amorphous content of the coatings is tiny, while the porosity is 2∼3 times different, and the porosity should be the dominant factor affecting the corrosion resistance of the coating.

Table 3

The electrochemical parameters of the heat-treated coatings.

Coating	OCP (mV)	E _corr (mV)	I _corr (A/cm²)
1#	−499.56	−244	3.796 × 10⁻⁶
1-1#	−463.89	−238	9.285 × 10⁻⁷
1-2#	−359.46	−229	8.537 × 10⁻⁷
2#	−332.47	−317	5.405 × 10⁻⁶
2-1#	−399.35	−290	3.732 × 10⁻⁶
2-2#	−384.56	−275	2.474 × 10⁻⁶
3#	−414.33	−298	4.703 × 10⁻⁶
3-1#	−439.53	−281	2.956 × 10⁻⁶
3-2#	−375.16	−264	1.345 × 10⁻⁶

The previous experimental results show that the amorphous content decreases in the following order: coating 1# = coating 1-1# > coating 1-2#, and the porosity decreases in the following order: coating 1# > coating 1-1# > coating 1-2#. In order to further explore whether the amorphous content or the porosity dominates the corrosion resistance of the coating, the EIS test has been performed on the coating 1#, 1-1#, and 1-2# which have better corrosion resistance, and the results are shown in Figure 7. R(Q(R)) is used as a model for the equivalent circuit EIS data fit, in which R _s, CPE1 and R _corr represent the solution resistance, constant phase element, and Faradaic impedance, respectively. Figure 7(a) is the Bode plot of impedance value |Z| versus frequency, and the inset is the fitted circuit. When alternating electric potentials of different frequencies act on the electrochemical system, the impedance value of the system will change with the frequency of the potential. The low-frequency impedance value can reflect the corrosion resistance of the system, the rule of which is generally that the larger the low-frequency impedance of the system, the better the corrosion resistance of the material [42]. Therefore, the resistance values of coatings with different process parameters decreased in the following order: coating 1-2# > coating 1-1# > coating 1#, which is consistent with the conclusion of the electric polarisation curve. Figure 7(b) exhibits the Bode plot of phase angle versus frequency, and all three coatings have only one peak, which means that the test system has only one time constant [43]. Figure 7(c) illustrates the Nyquist plot of the coatings in 3.5 wt.% NaCl solution. Generally, the diameter of the Nyquist diagram is related to the corrosion resistance of the coatings, and the rule is that the larger the diameter, the better the corrosion resistance of the coatings [44]. The diameters of the curves of different coatings decrease in the following order: coating 1-2# > coating 1-1# > coating 1#, which again proves that coating 1-2# has the best corrosion resistance. The above EIS test results show that when the amorphous content is not much different, porosity is the dominant factor affecting the corrosion resistance of the coatings.

Table 4 lists the parameters of the EIS fitting circuit, where the polarisation resistance R _corr can characterise the corrosion resistance of the coatings. The larger the R _corr, the smaller the corrosion rate [43], which further confirms that coating 1-2# has the best corrosion resistance. In addition, the chi-square χ² is a parameter for evaluating the systematic error, and the χ² is in the range of 10⁻⁴∼10⁻³, indicating that the equivalent circuit is reasonable and the fitting result is reliable.

Table 4

The equivalent circuit parameters of the heat-treated coatings.

Coating	R _s (Ω·cm²)	R _corr (Ω·cm²)	CPE1-T (µF·cm⁻²)	CPE1-P (µF·cm⁻²)	χ ²
1#	53.03	23763	1.9472 × 10⁻⁵	0.56376	3.6 × 10⁻⁴
1-1#	65.38	25205	1.9097 × 10⁻⁵	0.58495	4.6 × 10⁻⁴
1-2#	76.14	27593	2.1783 × 10⁻⁵	0.46179	6.8 × 10⁻⁴

Figure 8 shows the corrosion morphology of the surface of the coating 1#, 1-1#, and 1-2# after being corroded in 3.5wt.% NaCl solution. In terms of the degree of corrosion, there is no obvious corrosion trace on the surface of the three coatings, indicating that the corrosion resistance of these coatings is excellent. The coating 1# has the largest area of corrosion traces, while the coating 1-2# can hardly see the corroded traces, and the corrosion degree of the coatings 1-1# is between the two, with only one shallow corrosion pit, which verifies the conclusion that the corrosion resistance decreases in the following order: coating 1-2#>coating 1-1#>coating 1#. On the whole, the heat treatment process with temperature of 200°C and time of 30 min can most obviously improve the corrosion resistance of the Fe-based amorphous composite coatings.

Conclusion

The laser cladding coatings were heat treated with different temperatures, and new Fe-based amorphous composite coatings were obtained. The effects of the temperature on the amorphous content, morphology, microstructure, microhardness, and corrosion resistance of coatings were systematically studied. It is found that heat treatment at a suitable temperature can effectively solve the defects of coatings prepared by laser cladding, improving the comprehensive properties of coatings. The main results of the research are as follows:

The main phase composition of Fe-based amorphous composite coatings after heat treatment includes the amorphous phase, solid solution Fe-Cr, and hard phases B₆Fe₂₃ and Cr₂B. When the temperature is 150°C, the amorphous content of the coatings remains unchanged. With the increase in heat treatment temperature, the amorphous content of the coatings decreases.

After heat treatment, the pores in the cross-section of Fe-based amorphous composite coatings greatly reduce with almost no cracks, and the pores decreases with the increase of heat treatment temperature. When the temperature is 150°C, the number of grains in the coatings does not change, but when the temperature is 200°C, the number of grains in the coating increases significantly, and the amorphous region decreases.

The microhardness of the coating 1# and 2# do not change significantly after heat treatment, while the microhardness of the coating 3# increases. It may be due to the formation of more hard phases in coating 3# after heat treatment, while the hard phases of the coating 1# and 2# have reached saturation, so their microhardness can not be increased.

The corrosion resistance of Fe-based amorphous composite coatings is slightly improved after heat treatment, which rises with the increasing temperature. The corrosion resistance of the coating 1-2# is the best, because of the smaller porosity and the higher amorphous content. When the difference in amorphous content is slight, the porosity in the coatings becomes the dominant factor affecting the corrosion resistance of the coatings.

Footnotes

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

Original measurement data can be provided on request.

References

Luo

Sun

Jiao

Formation and tribological behavior of AC-HVAF-sprayed nonferromagnetic Fe-based amorphous coatings. Surf Coat Tech. 2018;334:253–260.

Zhang

Xing

Design of Fe-based bulk metallic glasses with improved wear resistance. ACS Appl Mater Inter. 2018;10(49):43144–43155.

Sharma R

Das R

Kumar S

Effect of chromium–titanium on corrosion and erosion of HVOF coating. Surf Eng. 2022;38(4):366–374.

Sharma

Das

Kumar

SR.

Microstructure, mechanical and tribological properties of high velocity oxy fuel thermal spray coating: A review. Materialwiss Werkst. 2023;54(1):90–97.

Sharma

Das

Kumar

SR.

Effect of varying chromium and titanium content on corrosion, mechanical and solid particle erosion properties of iron alloy based coating. Materialwiss Werkst. 2022;53(6):675–685.

Al-Abboodi

Fan

Mhmood

The dry sliding wear rate of a Fe-based amorphous coating prepared on mild steel by HVOF thermal spraying. J Mater Res Technol. 2022;18:1682–1691.

Liang

Zhou

Liu

Wettability and corrosion performance of arc-sprayed Fe-based amorphous coatings. Surf Coat Tech. 2022;433:128129.

Cui

Zhai

Microstructure and corrosion resistance of Fe-based amorphous coating prepared by detonation spray. Surf Coat Tech. 2020;399:126096.

Liang

Zhou

JS.

Preparation and characterization of laser cladded FeCrMoBSi amorphous composite coatings. Surf Coat Tech. 2021;423:127520.

10.

Sharma

Das

Kumar

SR.

Microstructure, adhesion and erosion properties of Fe-Cr-Ti-Mo-C-Si coating with varying titanium. Mater Today Commun. 2021;26:101826.

11.

Quazi

Fazal

Haseeb

ASMA

Effect of rare earth elements and their oxides on tribo-mechanical performance of laser claddings: A review. J Rare Earth. 2016;34(6):549–564.

12.

Liu

Chen

. Research and development status of laser cladding on magnesium alloys: a review. Opt Laser Eng. 2017;93:195–210.

13.

Wang

Zhang

Gong

Microstructures and corrosion resistance of Fe-based amorphous/nanocrystalline coating fabricated by laser cladding. J Alloy Compd. 2017;728:1116–1123.

14.

Zhu

Wang

Synthesis of Fe-based amorphous composite coatings with low purity materials by laser cladding. Appl Surf Sci. 2007;253(17):7060–7064.

15.

Hong

YS.

Fe-based thick amorphous-alloy coatings by laser cladding. Surf Coat Tech. 2001;141(2-3):141–144.

16.

Dai

Zhang

Distinction in corrosion resistance of selective laser melted Ti-6Al-4 V alloy on different planes. Corros Sci. 2016;111:703–710.

17.

Jiao

Luo

Wei

Influence of sealing treatment on the corrosion resistance of Fe-based amorphous coatings in HCl solution. J Alloy Compd. 2017;714:356–362.

18.

Wang

Cheng

Yang

JY.

Influence of laser remelting on organization, mechanical properties and corrosion resistance of Fe-based amorphous composite coating. Surf Coat Tech. 2021;414:127081.

19.

Ghotbi

Abbasi

Effect of the second heat treatment on the porosity and conductivity of a template-synthesized carbon material for use in supercapacitor electrodes. Solid State Sci. 2022;128:106871.

20.

Al-Shelkamy

Abu Hashish

Salama

Influence of heat treatment on the mechanical and the lubricant wear characteristics of stainless-steel grades against 5 wt% NaCl as industrial shielding materials. Appl Radiat Isotopes. 2022;188:110361.

21.

Miao

Fang

Shi

Coupling effects of boron nitride and heat treatment on crystallization, mechanical properties of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV). Polymer. 2022;252:12496.

22.

Luan

Bamboo heat treatments and their effects on bamboo properties. Constr Build Mater. 2022;331:127320.

23.

Chen

Zhao

Zhang

Metastable phase evolution and nanoindentation behavior of amorphous Ni-Cu-P coating during heat treatment process. J Alloy Compd. 2019;805:597–608.

24.

Huang

Kang

Yue

Effect of heat treatment on erosion-corrosion of Fe-based amorphous alloy coating under slurry impingement. J Alloy Compd. 2020;820:153132.

25.

Zheng

Sun

Effect of heat treatment on the structure, cavitation erosion and erosion-corrosion behavior of Fe-based amorphous coatings. Tribol Int. 2015;90:393–403.

26.

Wang

Ding

Effects of heat treatment on HVOF-sprayed Fe-based amorphous coatings. Surf Eng. 2021;37(5):590–598.

27.

Coimbrão

Zepon

Koga

Corrosion properties of amorphous, partially, and fully crystallized Fe₆₈Cr₈Mo₄Nb₄B₁₆ alloy. J Alloy Compd. 2020;826:154123.

28.

Nayak

Kumar

Pathak

Multi-scale mechanical properties of Fe-based amorphous/nanocrystalline composite coating synthesized by HVOF spraying. J Alloy Compd. 2020;825:154120.

29.

Zhai

Tian

Fabrication of Fe-based amorphous composite coating by laser cladding. J Non-Cryst Solids. 2022;589:121648.

30.

Borrego

Blázquez

Lozano-Pérez

Structural relaxation in Fe(Co)SiAlGaPCB amorphous alloys. J Alloy Compd. 2014;584:607–610.

31.

Kang

Chen

Wen

Effects of structural relaxation and crystallization on the corrosion resistance of an Fe-based amorphous coating. J Non-Cryst Solids. 2020;550:120378.

32.

Liu

Shieu

Hsiao

WT.

Enhancement of wear and corrosion resistance of iron-based hard coatings deposited by high-velocity oxygen fuel (HVOF) thermal spraying. Surf Coat Tech. 2014;249:24–41.

33.

Kumar

Nayak

Bijalwan

Optimization of mechanical and corrosion properties of plasma sprayed low-chromium containing Fe-based amorphous/nanocrystalline composite coating. Surf Coat Tech. 2019;370:255–268.

34.

Shu

Liu

Zhao

Structure and high-temperature property of amorphous composite coating synthesized by laser cladding FeCrCoNiSiB high-entropy alloy powder. J Alloy Compd. 2018;731:662–666.

35.

Yang

Zhang

Peng

Effects of crystallization on the corrosion resistance of Fe-based amorphous coatings. Corros Sci. 2012;59:10–19.

36.

Guo

Zhang

Yang

Corrosion and wear resistance of a Fe-based amorphous coating in underground environment. Intermetallics. 2012;30:94–99.

37.

Zhou

Liao

Effect of laser remelting on microstructure and properties of WC reinforced Fe-based amorphous composite coatings by laser cladding. Opt Laser Technol. 2018;103:8–16.

38.

Yang

Fan

Wang

Effect of Nb content on corrosion behavior of Ti-based bulk metallic glass composites in different solutions. Appl Surf Sci. 2019;471:108–117.

39.

Ren

Cheng

Feng

Experimental study on corrosion-fouling relationship of Ni-W-P composite coating surface of heat exchanger. Surf Topogr-Metrol. 2019;7(1):15011.

40.

Zhang

Chan

Pitting initiation in Fe-based amorphous coatings. Acta Mater. 2012;60(10):4152–4159.

41.

Qin

Zhang

Long-term corrosion behavior of HVOF sprayed FeCrSiBMn amorphous/nanocrystalline coating. T Nonferr Metal Soc. 2015;25(4):1144–1150.

42.

Song

Kong

DJ.

Microstructure and corrosion behaviours of composite coatings on S355 offshore steel prepared by laser cladding combined with micro-arc oxidation. Appl Surf Sci. 2019;497:143703.

43.

Wei

Dong

Zhou

Influence of the secondary phase on micro galvanic corrosion of low carbon bainitic steel in NaCl solution. Mater Charact. 2018;139:401–410.

44.

Wang

Cheng

Zhang

Effect of laser scanning speed on microstructure and properties of Fe based amorphous/ nanocrystalline cladding coatings. Mater Chem Phys. 2020;250:123091.

Original coating (#)	Temperature (°C)	Time (min)	New no. (#)
1	150	30	1-1
1	200	30	1-2
1	250	30	1-3
2	150	30	2-1
2	200	30	2-2
2	250	30	2-3
3	150	30	3-1
3	200	30	3-2
3	250	30	3-3

Original coating (#)	Temperature (°C)	Time (min)	New no. (#)
1	150	30	1-1
1	200	30	1-2
1	250	30	1-3
2	150	30	2-1
2	200	30	2-2
2	250	30	2-3
3	150	30	3-1
3	200	30	3-2
3	250	30	3-3

Original coating (#)	Temperature (°C)	Time (min)	New no. (#)
1	150	30	1-1
1	200	30	1-2
1	250	30	1-3
2	150	30	2-1
2	200	30	2-2
2	250	30	2-3
3	150	30	3-1
3	200	30	3-2
3	250	30	3-3