Wenlong Zhou

Effect of wet shot peening on Ti-6Al-4V alloy treated by ceramic beads

Abstract Ti-6Al-4V alloy was processed by wet shot peening with ceramic beads. The effects of the shot peened intensity on the microstructure, surface morphology, and residual stress were investigated. A tensile–tensile fatigue test was performed and the fracture mechanism was proposed. The results demonstrate that the surface roughness after wet shot peening is obviously lower than that after dry shot peening. With the increase of the shot peened intensity, the depth of the residual stress layer increases to 250 μm, and the maximum stress in this layer increases to –895 MPa. The fatigue strength also increases by 12.4% because of the wet shot peening treatment. The dislocation density of the surface layer is significantly enhanced after the wet shot peening with ceramic beads. The microstructure of the surface layer is obviously refined into ultra-fine grains.

Direct Friction Welding of TiAl Alloy to 42CrMo Steel Rods

The effect of post-weld heat treatment (PWHT) on the mechanical properties and microstructure of direct friction-welded joint between TiAl alloy and 42CrMo steel rods was investigated in this paper. It was found that solid joint between TiAl alloy and 42CrMo steel could be obtained without adding interlayer. After PWHT at 580°C for 2 h, the tensile strength of the joint reached 405 MPa, and fracture happened through the TiAl alloy substrate with quasi-cleavage features. The tempered sorbite formed near the interface, improving the joint strength significantly. It was found that TiFe2, TiAl, and small amount of TiC brittle phases formed at the interface, and the interfacial layer was as thin as 2–5 µm. The precipitated phases were 1 µm in average size, and distributed discontinuously at the interface.

Microstructure and mechanical properties of friction welds between TiAl alloy and 40Cr steel rods

Direct friction welding of TiAl alloy to 40Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment (PWHT) states were investigated. The martensitic transformation occurred and brittle TiC phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on TiAl alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiAl alloy side, but the as-welded specimen failed through the interface.

Effect of electropulsing on deformation behavior of Ti–6Al–4V alloy during cold drawing

Abstract Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to investigate effect of electropulsing on microstructure and texture evolution of Ti–6Al–4V during cold drawing. Research results demonstrate that the electropulsing treatment (EPT) can enhance the deformability of the grains with unfavorable orientations, which makes the compatibility of deformation among grains much better. A comparison in texture evolution between conventional cold drawing and EPT cold drawing indicates that the EPT promotes prismatic «a» slip moving, restricts pyramidal «c+a» slip occurring and accommodates the deformation with c-component by grain boundary sliding. The fraction decrease of low-angle grain boundaries for samples deformed with EPT reveals that the application of electropulsing restricts the formation of the incidental dislocation boundaries and the geometrically necessary boundaries.

Atomic interdiffusion in Ni–Cu system under high magnetic field

Abstract The effect of high magnetic field on the atomic interdiffusion in Ni–Cu system was studied using the Cu/Ni/Cu diffusion couples. During the atomic interdiffusion in Ni–Cu system, it was found that the interdiffusion coefficients increased with the increase of molar fraction of Ni atoms in the interdiffusion zones when the couples were annealed with or without the magnetic field. It was noted that all corresponding interdiffusion coefficients under the magnetic field are smaller than those without the magnetic field. The results demonstrate that the magnetic field retards the atomic interdiffusion in Ni–Cu system. This retardation is achieved through reducing the frequency factors but not changing the interdiffusion activation energies.

Mechanical properties of strengthened surface layer in Ti–6Al–4V alloy induced by wet peening treatment

Abstract A modified surface layer was formed on Ti–6Al–4V alloy by wet peening treatment. The variations of the residual stress, nano-hardness and microstructure of the modified layer with depth from surface were studied using X-ray diffraction analysis, nano-indentation analysis, scanning electron microscopy and transmission electron microscopy observations. The results show that both the compressive residual stress and hardness decrease with increasing depth, and the termination depths are 160 and 80 μm, respectively. The microstructure observation indicates that within 80 μm, the compressive residual stress and the hardness are enhanced by the co-action of the grain refinement strengthening and dislocation strengthening. Within 80–160 μm, the compressive residual stress mainly derives from the dislocation strengthening. The strengthened layer in Ti–6Al–4V alloy after wet peening treatment was quantitatively analyzed by a revised equation with respect to a relation between hardness and yield strength.