Over the years, the in-situ fabrication of metal matrix composites has been highly investigated owing to its high bonding strength with the matrix, pollution free interface and uniform particle distribution. Presently, metal matrix composites, such as titanium nitride (TiN) and titanium diboride (TiB2) in their particle reinforced phase, are being used in wear-resistant structural parts designed for ultra-high temperature conditions because of their high hardness, high melting point, good chemical stability at high temperatures, and good corrosion resistance and abrasion resistance at elevated temperatures. These TiN-TiB2 nanocrystalline coatings are usually prepared by laser cladding, plasma deposition and self-propagating high temperature synthesis techniques. Unfortunately, these techniques involve complicated operations and demand expensive equipment hence a high fabrication cost. An alternative has recently emerged where by argon arc welding presents a significantly impressive option. Several studies have already been published regarding argon arc welding, however, most of these studies primarily focus on the structure and properties of particles at the micrometer level. Therefore, it is imperative to study the variation of microstructures of the coatings and discuss the formation mechanisms under different processing conditions.
Recently, a team of researchers led by professor Jun-sheng Meng from the College of Naval architecture and Marine Engineering at Shandong Jiaotong University in China investigated the influence of the argon arc cladding parameters on the dilution rate, phase composition, microstructure, and properties of the coating. In order to achieve this, they purposed to employ the in-situ argon arc welding and rapid cooling methods to deposit titanium powder, boron nitride powder, and Ni60A powder on the surface of 35CrMnSi(structural steel bar) to synthesize nanocrystalline Nickel-based composite coatings. Their work is currently published in the research journal, Applied Surface Science.
Briefly, the researchers commenced the experimental work by cladding and processing the argon arc where the powders to be utilized were proportioned in molar ratios, dry mixed using planetary ball mill and protected from oxidation by being fed with argon. Next, the research team employed the calculating method where the analysis and calculation of the dilution ratio were determined. Eventually, the three researchers characterized the microstructures of the nanocrystalline coatings by means of X-ray diffraction meter, scanning electron microscopy and transmission electron microscopy.
Dilution ratios of the welded cross-section in the welding layer were obtained by assessing the effects of current variation and speed during the welding process. Additionally, the authors of this work observed that the reaction between the powders proceeded under low temperature conditions, at an increase welding speed, and fast cooling rate, thereby hindering the complete reaction of the Ti and BN powders. Moreover, they noted that a longer arc dwell time on the surface of the welding layer increased the driving force of growth, thereby resulting in faster and easier growth.
In their work, Jun-sheng Meng and colleagues showed that Nickel-based coating reinforced by in situ TiN and TiB2 nanocrystalline particles could be prepared on the surface of 35CrMnSi steel in the condition of selected welding technological parameters by AAC and achieve a good metallurgical bonding. Furthermore, their results showed that the welding technological parameters of nanocrystalline coatings had certain effects on the dilution ratio of the clad layer. At the end of it all, the nanocrystalline coatings showed better wear resistance properties than the 35CrMnSi steel. The refinement of the TiN and TiB2 particle size prove the distinct improvement of surface mechanical properties. For example, The techniques can be applied to surface of bucket teeth and tooth block. The trial showed that in comparison with the tooth block (35CrMnSi steel) with no argon arc cladding, the service life of the argon arc cladding the tooth block (35CrMnSi steel)could be increased by 6 ~ 7 times.
Jun-sheng Meng, Guo Jin, Xiao-ping Shi. Structure and tribological properties of argon arc cladding Ni-based nanocrystalline coatings. Applied Surface Science, volume 431 (2018) pages 135–142.Go To Applied Surface Science