无氢渗碳层对TC4钛合金力学性能的影响

Influence of Hydrogen-free Carburized Coating on Mechanical Properties of TC4 Titanium Alloy Substrate

TC4钛合金经过渗碳后,表面硬度提高了2.84倍。经过1,2,3 h处理后的带渗层、不带渗层(热处理)的样品抗拉强度、规定非比例延伸强度与原始样相当;3种热处理(即不带渗层)断后伸长率和断面收缩率优于原始样,带渗层样的断后伸长率和断面收缩率有较大下降,并随着时间的延长,断后伸长率和断面收缩率下降。带渗层样在拉断过程中,外表面渗层不断剥落,外表面布满环状裂纹,裂纹自根部向中间逐渐增加,根部为细小裂纹,愈向中间裂纹愈宽大;随着时间的延长,裂纹主要集中在断口附近,试样根部较少。热处理的TC4样品断口为塑性断裂,位错滑移在断裂过程中起重要作用;带渗层样品接近于外表面表现为脆性断裂特征,心部为塑性断裂。

The hardness of the alloy surface after carburizing increases by 2.84 times. Through 1 h, 2 h, and 3 h treating,the tensile strength and nonproportional extension strength are similar to those of the original sample. After the three heat treatment （without carburized layer） elongation and reduction of area on the cross section are better than those of the original sample, but the sample with carburized layer are heavily decreased, and with the time extension, the elongation and the reduction of area decline. In the tensile process, the outer surface layer, covered with ring-shaped cracks, flakes off gradually. The cracks are increased from the root to the middle. There are small cracks on the root while the cracks become wider and larger in the middle. The cracks mainly concentrate near the fracture, and a few on the root. The fracture of the heat-treated TC4 sample is plastic fracture, and the dislocation slip plays an important role in the fracture process. The layer close to the outer surface of the sample shows brittle fracture characteristics, the core is of plastic fracture, and the fracture direction can be determined by the fracture morphology.