Weiping Tong

An Evaluation of a Borided Layer Formed on Ti-6Al-4V Alloy by Means of SMAT and Low-Temperature Boriding

In this paper, a nanocrystalline surface layer without impurities was fabricated on Ti-6Al-4V alloy by means of surface mechanical attrition treatment (SMAT). The grain size in the nanocrystalline layer is about 10 nm and grain morphology displays a random crystallographic orientation distribution. Subsequently, the low-temperature boriding behaviors (at 600 °C) of the SMAT sample, including the phase composition, microstructure, micro-hardness, and brittleness, were investigated in comparison with those of coarse-grained sample borided at 1100 °C. The results showed that the boriding kinetics could be significantly enhanced by SMAT, resulting in the formation of a nano-structured boride layers on Ti-6Al-4V alloy at lower temperature. Compared to the coarse-grained boriding sample, the SMAT boriding sample exhibits a similar hardness value, but improved surface toughness. The satisfactory surface toughness may be attributed to the boriding treatment that was carried out at lower temperature.

Thermal Stability of Nanocrystalline BCC-Ti Formed by Phase Transformation During Surface Mechanical Attrition Treatment

This paper reports the transformation of HCP-Ti into BCC-Ti in the Ti–6Al–4V alloy induced by surface mechanical attrition treatment (SMAT). The processes of surface nanocrystallization (SNC) and phase transformation were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the average grain size in the surface layer gradually decreased with increasing SMAT duration, but plateaued at 10nm after 90min of SMAT, while the proportion of BCC-Ti in the surface layer gradually increased. The refined grains displayed equiaxed grain morphology with a random crystallographic orientation. The thermal stability of nanocrystalline BCC-Ti was investigated by subjecting it to isothermal annealing treatment in the temperature range of 450–800∘C. BCC-Ti nanocrystallites were shown to exhibit excellent thermal stability up to 650∘C, whereas those in HCP-Ti started to recrystallize at approximately 550∘C.

Simultaneous nitriding for two components of Ti/steel clad sheet

Abstract Nanostructured surface layers were fabricated on titanium and steel components of the Ti/steel clad sheet by the surface mechanical attrition treatment (SMAT). The average grain size on the top surface layer of SMAT titanium component and SMAT steel component is ∼8 and 10–20 nm respectively. Subsequently, the nitriding behaviours of the SMAT Ti/steel clad sheet at 530°C for 8 h were investigated in comparison with those of the coarse grained counterpart. Experimental results showed that the surface nanocrystallisation evidently promotes the formation of an ultrafine polycrystalline compound layer on titanium component and of a much thicker compound layer on steel component. Surface property tests demonstrated that two components of the SMAT nitrided Ti/steel clad sheet exhibit high surface hardness and excellent wear resistance. This paper offers a novel approach for simultaneous nitriding of two components on the Ti/steel clad sheet.

The Effect of Mechanical Shot Blasting in Producing the Surface Ultrafined Grain Layer on Large-Size Titanium Plate

This paper reported that the mechanical shot blasting was a feasible method for producing ultra-fined grain layer on large-size titanium plate. The MSB effects on producing ultra-fined layer were investigated by optical microscopy, X-ray diffraction, transmission electron microscopy, and micro-hardness tester. The experimental results showed that the thickness of the surface severe plastic deformation layer increased with the improvement in processing speed, but presented stabilization with prolonging the processing durations. The maximum thickness of the ultra-fined grain layer was about 320 μm, and the minimum grain size in the topmost surface was about 180 nm. The ultra-fined grain presented equiaxed grain morphology with random crystallographic orientation.