Ti6Al4V表面激光改性层重熔处理的微观组织特征及宽温域摩擦学性能研究

采用激光复合工程技术对Ti6Al4V基体表面进行强化耐磨处理，首先在Ti6Al4V合金表面进行激光氮化Ti(N)]和氮氧化Ti(N,O)]处理，然后在纯氩气气氛中分别对Ti(N)层和Ti(N,O)层进行激光重熔处理，制备了组织分布更为均匀的重熔氮化层Re-Ti(N)]和重熔氮氧化层Re-Ti(N,O)]. 组织结构分析揭示了Re-Ti(N)层主要由富氮αˊ-Ti和TiN_x组成，而Re-Ti(N,O)层则主要由富氧αˊ-Ti和TiN_xO_y组成. 相对于Ti6Al4V基体，Re-Ti(N)层和Re-Ti(N,O)层的硬度、弹性模量和磨损量降低了2倍以上，然而激光复合处理前后材料均表现出较大的摩擦系数. 相对于Re-Ti(N)层，氧原子的加入，不仅能够有效细化组织和提升强韧度，而且显著抑制了摩擦界面的黏着磨损. 通过磨屑结构分析进一步验证了基体黏着磨损机制和重熔改性层磨粒磨损机制. 

Microstructure Characteristics and Wide Temperature Range Tribological Properties of Ti6Al4V Laser Modified Surface by Remelted

A two-step approach toward creating hard, wear-resistant layer on Ti6Al4V was conducted. Laser remelting process was applied on the in-situ formation of nitirided Ti(N)] layer and oxynitrided Ti(N,O)] layer on Ti6Al4V that was prepared by the laser gas-assisted processing, resulting Re-Ti(N) and Re-Ti(N,O) displayed the relatively uniform hierarchy, respectively. The results revealed that, Re-Ti(N) layer had the composite structure comprised of nitrogen-rich αˊ-Ti and TiN_x, while Re-Ti(N,O) layer had a highly specific heterogeneous structure composed of nitrogen and oxygen-rich αˊ-Ti, TiN_xO_y. As compared with Ti6Al4V, the hardness, elastic modulus and wear resistance of Re-Ti(N) and Re-Ti(N,O) increased by 2 times. In comparison with Re-Ti(N) layer, the introduction of oxygen not only enabled refining the crystalline structure and promoting the mechanical strength of Re-Ti(N) layer significantly, but also inhibited the happening of adhesive wear between the sliding contact; neverthless the friction remained relatively higher regardless of the surface processing over Ti6Al4V. According to the analysis of wear debris collected from the friction testing, the high dislocation density and defects induced by plastic deformation during friction were figured out to be the crucial factors for the wear mechanism of Ti6Al4V before and after surface process. Evolution of the frictional behavior Ti6Al4V before and after laser processing was further clarified on the basis of the microstructural transformation and thermal properties of Ti6Al4V against the counterpart.