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研究

Effect of heat treatment conditions on microstructure evolution and mechanical properties of Zr -2.5 Nb Alloy

摘要:

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,与水冷的发生的切变型相变相比,空冷和炉冷均发生扩散型转变,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,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；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。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。

Abstract:

The hot-rolled Zr-2.5 Nb alloy plate are 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 are studied.The results show that there are two different diffusion transformation in the air-cooling and furnace-cooling process compared with water-cooling. In the air-cooling process, nano-scale lath αs phase is precipitated inside the β phase to form the bimodal microstructure. During the furnace cooling process, α_p phase directly consumes β phase and grows up to form equiaxed microstructure.With the increase of heat treatment temperature and the holding time, the volume fraction of α_p phase decreased, the continuity of β_trans phase increased and α_s phase coarsening in air-cooling process, The volume fraction of α_p phase in the equiaxed microstructure in furnace-cooling process remains basically unchanged, the average grain size increases, and the continuity of the residual β phase is enhanced. Compared with the equiaxed microstructure, the nano-α_s phase in the bimodal microstructure improves the strength of the alloy and the α_p 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.