An investigation is reported on crack-free laser clad Fe-based alloy by use of biaxial powder feeding shielded with argon gas. The microstructure and phase structure of the coating were studied, and ...mechanical properties were analyzed through hardness, tension strength and wear resistance of the coating. Microstructure analysis showed that there was retained austenite with spherical particles distributed therein in the interdendritic and nearby grain boundary regions. The mechanical test results showed that net-like distributed retained austenite in the interdendritic region had certain toughening effect through blunting crack-tip. Under wear condition of high sliding speed and high loading, the wear resistance of the coating with net-like retained austenite was much higher than that of the coating with some discontinuous carbide network or carbide blocks. The results showed that toughening of laser clad Fe-based alloy with high hardness over 850
HV could be achieved by modifying interdendritic phases from net-like carbide to net-like austenite with spherical particles.
The growth and propagation behavior of austenite-to-bainite isothermal transformation in laser-cladded, Si-rich, and Fe-based coatings is investigated. The crystallographic features, orientation ...relationship at different isothermal temperatures, and the morphology of the nanostructured bainite are determined. The Nishiyama-Wassermann type orientation relationship is observed at a high temperature and at a low temperature, and mixed Nishiyama-Wassermann and Kurdjumov-Sach mechanisms are seen. The growth direction is investigated by the partial dislocation theory and an extrapolated model based on the repeated formation of lenticular-shaped subunits and pile-up along the close-packed directions of the close-packed planes. The variants of the bainite growth directions would be more selective at the high transformation temperature.
Nano-Al2O3/Ni brush plated composite coatings were prepared by co-deposition of Al2O3 nanoparticles with Ni metal matrix during brush plating. In this process nanocrystalline ceramic powders with ...grain sizes below 40 nm were suspended in the plating solution and deposited with the metal to produce nanoparticle strengthened metal matrix composite coatings. The microstructure, composition, microhardness and wear properties of the coating in abrasive contaminant lubrication were examined. The results show that the nanoparticles are uniformly distributed in the composite coating, and the microstructure of the composite coating is much finer and denser compared with the pure nickel plating coating. Moreover, the microhardness and tribological properties of the composite coating are higher than that of the pure nickel coating. Substrate: 1045.
To improve the corrosion resistance and surface conductivity of stainless steel bipolar plate, C/Al–Cr–N multilayer coatings with varying Al:Cr target current are deposited on stainless steel 316L ...(SS316L) by magnetron sputtering. Scanning electron microscope (SEM) results show that the coating is about 2.3μm in total thickness, consisting of 0.9μm carbon layer and 1.4μm Al–Cr–N sub-layer. The interfacial contact resistance (ICR) result indicates that the surface resistance decreases with the increasing content of chromium, and achieves the minimum value of 6.17–4.88mΩ-cm2 at the compaction force between 120 and 150Ncm−2 for the Al2Cr4 sample. The electrochemical and inductively coupled plasma atomic emission spectrometry (ICP-AES) results disclose that C/Al–Cr–N multilayer coatings with Cr:N atomic ratio of 1:1 and lower aluminum content have higher chemical inertness and better corrosion resistance. Al6Cr0 and Al5Cr1 samples exhibit more negative corrosion potential and higher passive current density with galvanic corrosion on the surface due to the existence of AlN phase. Therefore, C/Al–Cr–N multilayer coatings with lower aluminum content are preferred for bipolar plate application.
•C/Al–Cr–N multilayer coatings are deposited on SS316L by magnetron sputtering technique.•C/Al2Cr4N sample has the lowest ICR, being 6.17–4.88mΩ-cm2 at the compaction force of 120–150Ncm−2.•Coatings with Cr:N atomic ratio of 1:1 and low Al content have better corrosion resistance.•Coatings with Cr:N atomic ratio of 1:1 and low Al content are preferred for bipolar plate.
► Firstly find the tadpole-shape precipitates in the welding joint. ► The precipitation strengthening can account for 79% of the total strength. ► The results can provide some insights on the ...application of Mg-RE alloy.
In this study, the effects of heat treatments on the quality of laser welded Mg-rare earth alloy NZ30K were systematically studied. The microstructure and mechanical properties of joints, welded by a 15
kW high power CO
2 laser, under different heat treatments had been tested and analyzed. The results indicated that the heat treatment plays an important role in the mechanical strength of laser welded joint of NZ30K. The microstructure of samples after the solution treatment as well as aging treatment is different from that of the as-received welded joint. For solution treatment, although the microstructure is much different from that of as-received welded joint, the solution strengthening effect is not obvious. There are lots of precipitates in the fusion zone after the aging treatment, which will significantly enhance the ultimate tensile strength (UTS) and the yield tensile strength (YTS) of the welding joint. 79% of YTS is caused by precipitation strengthening. Therefore, the results implied that the UTS and YTS can be greatly improved by proper heat treatment.
Softening in overlapping passes by laser-overlapped scanning surface hardening is a difficult problem of laser surface modification. Despite the advantage of laser quenching, softening in overlapping ...zone limits its practical application. In this paper, 45, 9Cr2Mo and W18Cr4V steel were hardened by laser-overlapping quenching. Softening occurred in all overlapping zones. The results of hardness testing indicated the softening width of 45 steel was the broadest and that of W18Cr4V steel was the narrowest. Different mixed microstructures composed the overlapping zone for three steels, i.e., tempered sorbite and a little tempered martensite in 45 steel, tempered martensite, tempered sorbite and a small amount of carbides in 9Cr2Mo steel, tempered martensite and a little carbide in W18Cr4V steel. The effect of activation energy of diffusion for carbon in steel and cooling rate on the decomposition of martensite have been investigated by developing a diffusion model based on the principle of carbon diffusion in martensite. The results indicated that action energy for diffusion of carbon in steel plays a main role in hindering decomposition of carbide and cooling rate has a limited action in reducing temper softening during laser-overlapping scanning.
The microstructural evolution of laser-welded 960 MPa grade high strength steel joints and its effect on softening behavior of heat affected zone (HAZ) were investigated in this paper. The results ...show that microstructure of HAZ and fusion zone (FZ) is composed of lath martensite and bainitic ferrite. The microstructure of mixed grained zone presents strip-like characteristics and small block martensite distributes along the grain boundary. The grain size near the fusion line is about 25 μm, and the grain size in the fine grain zone is less than 5 μm. Microhardness of HAZ and FZ is lower than base metal. The soft zone locates in transitional region between tempering zone and mixed grained zone due to the interaction of the martensite tempering and the recovery and recrystallization of the rolled microstructure. Microhardness of soft zone is 310 HV and drops 18% compared to base material. Welding heat input has a remarkable effect on the width of soft zone and microhardness. The tensile properties of weld joints are closely related to the softening behavior of HAZ.
5052 aluminum alloy sheets and galvanized mild steel sheets were joined in lap configuration by alternate-current double pulse gas metal arc welding with pure Al, Al–5Si, Al–12Si and Al–4.5Mg (wt%) ...filler wires. The effect of alloying elements on the microstructure of intermetallic compounds (IMC) layers formed between weld seam and steel, and tensile strength of the resultant joints were investigated. The thickness of IMC layer in all samples varied along the cross-section of the joint, the intermediate part of the IMC layer was thicker than the head and root parts. The diffusion of Si into Fe2Al5 sub-layer could restrain the growth of Fe2Al5 sub-layer and IMC layer, and joint's mechanical property improved with the increasing Si content in Fe2Al5 phase. Due to the high hot crack sensitivity of Al–4.5Mg alloy, cracks generated at the root of joint made with Al–4.5Mg filler, resulting in poor mechanical property.
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