累积叠轧Nb/Zr层状复合板的微观组织与力学性能研究

Microstructure and mechanical property of multilayered niobium/zirconium composites processed by accumulative roll bonding

摘要:

采用累积叠轧法制备了初始Zr层厚度不同的两种Nb/Zr金属层状复合板并对其在叠轧过程中的微观结构、织构演化和力学性能进行了研究。结果显示, Nb/Zr层状复合材料的界面结合良好,异质界面处无金属间化合物产生。随着叠轧道次增加,层状复合结构内部形成了贯穿于多个金属层的剪切带组织,初始Zr层厚度为1 mm的复合板较Zr层厚度为2 mm的复合板易于发生Zr层的颈缩、断裂和分离。Nb层内主要为位错胞状结构, Zr层内为高位错密度晶粒与动态回复晶粒的混合组织。此外,不同初始Zr层厚度的复合板中Nb层的织构演化特征不同：当初始Zr层厚度为1 mm时,Nb表现为强立方取向；当初始Zr层厚度为2 mm时,随着叠轧道次增加,旋转立方取向始终为主导的织构组分。两种复合板中Zr层的织构演化特征一致,即经一道次叠轧后,{0001}基面双峰织构为主要织构组分。随着叠轧道次增加,基面双峰织构略有减弱,同时出现了较弱的{11-20}丝织构。单轴拉伸测试表明,随着叠轧道次增加两种不同Zr层厚度的复合板屈服强度和抗拉强度均逐渐增大,而塑性延伸率呈现先减小后增大的趋势。经三道次叠轧后两种复合板的最大延伸率分别为14.2%和16.5%。叠轧过程中各金属显著的晶粒细化、Zr层内高位错密度晶粒与动态回复晶粒共存的混合组织以及Zr织构的特征演化是贡献于复合板具有高强度和良好塑性的原因。

Abstract:

In this work, multilayered niobium/zirconium (Nb/Zr) composites with different initial Zr thicknesses were processed by accumulative roll bonding (ARB). Microstructure, texture and mechanical property of the composites at different ARB cycles were systematically investigated. The results showed that the heterophase interfaces were well bonded and no intermetallic compounds formed. With increasing ARB cycles, shear bands formed cutting through the multiple metal layers. Necking and fracture of the Zr layers occurred preferentially in the composites with an initial Zr thickness of 1 mm. Dislocation cell structures were predominated in Nb layers, while a mixture consisting of grains with dense dislocations and dynamically recovered grains with a low dislocation density were predominant in Zr layers. In addition, texture evolution in Nb layers changed with varied initial thickness of Zr. When the initial Zr thickness was 1 mm, strong Cube orientation appeared in Nb layers. However, when the initial Zr thickness was 2 mm, rotated-Cube was the dominant texture in Nb layers with increasing ARB cycles. The textures in Zr layers were similar in the composites with different initial Zr thicknesses. After the first ARB cycle, the {10-13}<3032> orientation was the dominant texture. With increasing ARB cycles, this orientation was slightly weakened and minor {11-20} fiber texture developed. With the increase of the ARB cycles both yield strength and ultimate tensile strength increased monotonically for the composites with different initial Zr thicknesses. However, the maximum elongation firstly decreased and then increased with increasing ARB cycles. After the third ARB cycle, the maximum elongation reached 14.2% and 16.5% for the composites with the initial Zr thicknesses of 1 and 2 mm, respectively. The high strength and good plasticity of the composites originated from the significant grain refinement in the individual metals and the recovered Zr grains during ARB, together with the featured texture evolution in the Zr layers.