含氮气氛FSP表面改性纯钛的微结构和织构

Microstructure and texture of pure titanium surface modificated by friction stir processing

摘要:

本文研究了含氮气氛下FSP表面改性纯钛的微结构和织构。结果表明：FSP纯钛搅拌区为等轴晶粒,靠近AS侧和RS侧的动态再结晶晶粒平均晶粒尺寸为2.29μm,近表面和中心区受温升和摩擦搅拌的综合作用,平均晶粒尺寸分别长大至6.48μm和8.64μm。FSP热机影响区呈梯度分布,靠近搅拌区部分晶粒细化破碎严重；远离搅拌区部分,原始晶粒变形小,以形变孪生机制为主。AS侧、底部和RS侧的热机影响区宽度分别为900μm,700μm和480μm。热机影响区内主要形成{10-12}拉伸孪晶。搅拌针形状是FSP纯钛微区织构演变的重要影响因素,搅拌区晶粒的c轴接近于PD方向。受搅拌区晶粒细化和加工硬化共同作用,搅拌区硬度整体高于母材,硬度最大值达到223.7HV_0.5。

Abstract:

The microstructure and texture of FSP pure titanium in nitrogen atmosphere were investigated. The results showed that there were equiaxed grains in the stir zone. The average grain size of dynamic recrystallized grains near AS side and RS side was 2.29 μm. The combined effects of rising temperature and friction stir in the near surface and central zone, the average grain size grew to 6.48 μm and 8.64 μm respectively. The thermal-mechanical affect zone presented a gradient distribution. The grains near the stir zone had been seriously broken and refined. In the zone far away from the stir zone, the deformation of the original grains was slightly, and the deformation mechanism was dominated by deformation twinning. The width of the thermal-mechanical affect zone at AS side, bottom and RS side was 900 μm,700 μm and 480 μm respectively. The mainly deformation twins in the thermal-mechanical affect zone were {10-12} tensile twins. The structure of stirring pin was an important factor affecting the texture evolution of FSP pure titanium. Moreover, the c-axises of the grains in the stir zone were distributed close to the PD direction. Due to the combined effect of grain refinement and work hardening, the hardnesses in the stir zone were overall higher than the initial material, and the maximum hardness reached to 223.7HV0.5.