热处理工艺参数对双相Zr-2.5Nb合金组织演变机制及力学性能的影响

Effect of Heat Treatment Conditions on Microstructure Evolution and Mechanical Properties of Zr-2.5Nb Alloy

在α+β两相区高温区(750~850℃)对热轧态Zr-2.5Nb合金板材进行加热,保温不同时间(1~10h),随后以不同方式冷却至室温,研究热处理工艺参数对合金微观组织类型、显微组织特征(相含量、晶粒尺寸等)及力学性能的影响。结果表明,与水冷时发生的切变型相变相比,空冷和炉冷时均发生扩散型相变,其中空冷过程中β相内部析出纳米级板条状α_(s)相,形成双态组织;炉冷过程中α_(p)相直接消耗β相长大,形成等轴组织。随着热处理温度的升高和保温时间的延长,炉冷等轴组织中α_(p)相含量基本保持不变、平均晶粒尺寸增加,残余β相连续性增强;空冷双态组织中α_(p)相含量逐渐减小,β_(trans)相连续性增强,α_(s)相片层宽度增大。与炉冷等轴组织相比,空冷双态组织中纳米级α_(s)相使合金具有更高的强度、α_(p)相保证了良好的塑性,降低热处理温度、减少保温时间可使双态组织合金获得优异的强塑性匹配。

The hot-rolled Zr-2.5Nb alloys plates were heated in the high temperature region(750-850℃)of α+β two-phase region for different holding time(1-10 h)and then cooled to room temperature in different ways.The effects of different heat treatment conditions on the microstructure type,microstructure characteristic(phase content,grain size,etc.)and mechanical properties of the alloy were studied.The results show that there are two different diffusion transformation types in the air cooling and furnace cooling process compared with water cooling.In the air cooling process,nano-scale lathαs phase is precipitated inside the β phase to form the bimodal microstructure.During the furnace cooling process,αp phase directly consumesβphase and grows up to form equiaxed microstructure.With the increase of heat treatment temperature and the prolongation of holding time,the volume fraction ofαp phase decreases,the continuity ofβtrans phase increases andαs phase coarsening occurs in air cooling process.The volume fraction ofαp phase in the equiaxed microstructure in furnace cooling process remains basically unchanged,the average grain size increases,and the continuity of the residualβphase is enhanced.Compared with the equiaxed microstructure,the nano-αs phase in the bimodal microstructure improves the strength of the alloy and theαp phase ensures that the alloy has good plasticity.Reducing the heat treatment temperature and holding time can make the bimodal structure alloy have excellent combination of strength and plasticity.