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In this study, inspired by multilayer structures in nature, an equal weight ratio Ni/Cu composite sandwich specimen was introduced for joining 316 and NiTi alloys to improve the wear resistance of 316. The microstructural evolution process as well as the wear resistance mechanism is clarified by a series of material characterization methods and mechanical property tests. The microstructure of the Ni/Cu interlayer exhibits a dendritic morphology, and the NiTi layer shows both coarse and fine characteristics. The crystallography of 316-Ni/Cu–NiTi composite sandwich specimens was investigated by electron backscatter diffraction. Three types of friction balls (316, 440C, 100Cr6) were used to perform dry reciprocating sliding ball-on-plate wear testing on 316-Ni/Cu–NiTi composite sandwich specimens and 316 substrates under varying normal loads from 10 N to 30 N. The 316-Ni/Cu–NiTi specimens showed better wear resistance compared to the 316 substrate under different wear conditions, when the normal load is 30 N and the friction ball is 100Cr6, the specific wear rate of the coating is only 44% of the substrate. This study not only provides insights to enhance the wear resistance of 316, but also develops a novel approach to broaden the connection between austenitic stainless steel and NiTi alloys.

Multi-wire arc additive manufacturing (MWAAM) enabled customized production with high deposition efficiency and low cost as compared to the common wire arc additive manufacturing (WAAM) technology. In this paper, two titanium alloy components were prepared using the MWAAM technique, and the microstructures, mechanical properties, and wear behaviors of Ti–6Al–4V (TC4) alloy and Ti-6.5A1-3.5Mo-1.5Zr-0.3Si (TC11) alloy were investigated. The results showed that the microstructure distribution of TC11 alloy prepared by MWAAM was more intensive and the length and width of the lamellar α-Ti phase were significantly reduced compared with that of TC4 alloy. The polar densities corresponding to the texture in the two selected regions of the TC4 alloy and the TC11 alloy were 17.30 and 17.69, respectively. The proportion of the HAGBs of the TC4 sample and the TC11 sample were 99.07 % and 99.43 %, respectively. The average microhardness on the X–Y plane of TC4 and TC11 alloys were 316.17 HV and 366.14 HV, respectively, while the average microhardness on the Y-Z plane were 318.18 HV and 358.10 HV, respectively. The average compression yield strengths of TC4 and TC11 alloys were 836.61 MPa and 1088.33 MPa, respectively. The COFs of MWAAM TC4 and TC11 samples were stable at 0.479 and 0.455 under 20 N, respectively. The COFs of MWAAM TC4 and TC11 samples were stable at 0.472 and 0.432 under 60 N, respectively. The average yield strength, average ultimate strength, proportion of HAGBs, and microhardness of TC11 alloy were all higher than that of TC4 alloy. These results indicated that TC11 alloy had advantages over TC4 alloy in terms of mechanical properties and microstructure, with higher strength and deformation resistance. The properties of titanium alloy samples prepared by MWAAM were not lower than those of titanium alloy samples prepared by single wire WAAM, while MWAAM significantly better than single wire WAAM in deposition efficiency. The results obtained in this paper can help to prepare titanium alloy components with excellent mechanical properties more efficiently in MWAAM process.

Heterogeneous microstructure designs have attracted a great deal of attention, not only because they have the potential to achieve an ideal combination of two conflicting properties, but also because the processes involved in their fabrication are cost-effective and can be scaled up for industrial production. The process parameters in the preparation process have an important effect on the microstructure and properties of alloy members prepared by wire arc additive manufacturing (WAAM) technology. It was expected that the spatial heterogeneous microstructure with large microstructural heterogeneities in metals can be formed through changing the process parameters. In this work, homogeneous NiTi thin-walled component and heterogeneous NiTi thin-walled component were fabricated using WAAM technology by adjusting the heat input. The effects of deposition height and heat input on the microstructure, mechanical properties and wear properties of WAAM NiTi alloys were investigated. The results show that grains were gradually refined with the increase of deposition height in the homogeneous WAAM NiTi component. The ultimate tensile strength of homogeneous WAAM NiTi component increased from 606.87 MPa to 654.45 MPa and the elongation increased from 12.72% to 15.38%, as the increase of deposition height. Moreover, the homogeneous WAAM NiTi component exhibited excellent wear resistance, the coefficient of friction decreased from 0.760 to 0.715 with the increase of deposition height. Meanwhile, the grains in the heterogeneous WAAM NiTi component shows the finest grains in the central region. The ultimate tensile strength of the lower region, middle region and upper region of heterogeneous WAAM NiTi components were 556.12 MPa, 599.53 MPa and 739.79 MPa, and the elongations were 12.98%, 16.69%, 21.74%, respectively. The coefficient of friction for the lower region, middle region and upper region of heterogeneous WAAM NiTi components were 0.713, 0.720 and 0.710, respectively. The microhardness and cyclic compression properties of the homogeneous components with higher heat input were better than those of the heterogeneous components for the same deposition height. The tensile yield strength, elongation and wear resistance of the heterogeneous components were superior compared to the homogeneous components. These results can be used to optimize the WAAM process parameters to prepare NiTi components with excellent mechanical properties.

In this paper, the corrosion-wear-resistant alloy steel gradient material for camshaft was successfully prepared by direct laser deposition (DLD). The phase evolution, microstructure characteristics, microhardness, wear behaviors and corrosion resistance of alloy steel gradient material were studied using X-ray diffraction (XRD), electron backscatter diffraction (EBSD), hardness tester, wear tester and electrochemical workstation, respectively. The results showed that phase evolutions with the increase of stainless steel powders from α-Fe + Cr23C6 to α-Fe + Cr23C6 + (Cr, Fe)7C3. The microstructure of the alloy steel gradient material was refined with increasing the stainless steel powders. The preferred texture was weak with the increase of gradient due to the each layer experiencing a variety of complex thermal cycle effects. Meanwhile, the content of high-angle grain boundaries (HAGBs) and the volume fraction of Cr23C6 and (Cr, Fe)7C3 increased with gradient increasing, which promoted the toughness and enhanced the wear reaiatance of the material. In addition, the microhardness distribution of alloy steel gradient material showed a gradient increase from 281 HV to 795 HV along with deposition direction. The wear resistance and corrosion resistance of alloy steel gradient material were extremely improved. The average specific wear rate and corrosion current density of alloy steel gradient material specimen were 0.30 × 10−5 mm3/Nm and 1.3 × 10-7 A cm-2, respectively.