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充氢超高强度钢拉伸变形的原位中子衍射研究
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更新时间：2015-09-22
利用飞行时间法中子衍射对比研究了充氢与未充氢 1250 MPa 超高强度钢的拉伸变形行为与轴向晶格变形特征,
并观察了断口区组织形貌与晶粒取向特征. 在无加载条件下, 充氢试样的轴向(110)与(200)面间距分别大于与小于未充氢
试样的对应面间距, 显示出四面体间隙中氢原子的进入使轴向(110)面间距有所增加, 同时内部应力的平衡作用使轴向(200)
面间距有所减少. 未充氢试样在达到 1250 MPa 抗拉强度发生颈缩塑性断裂, 而含有 8.010-6可扩散氢的试样在分步加载至 500 MP
充氢超高强度钢拉伸变形的原位中子衍射研究TENSILE DEFORMATION BEHAVIOR OF HYDROGEN CHARGED ULTRAHIGH STRENGTH STEEL STUDIED BY IN SITU NEUTRON DIFFRACTION
利用飞行时间法中子衍射对比研究了充氢与未充氢 1250 MPa 超高强度钢的拉伸变形行为与轴向晶格变形特征, 并观察了断口区组织形貌与晶粒取向特征. 在无加载条件下, 充氢试样的轴向(110)与(200)面间距分别大于与小于未充氢试样的对应面间距, 显示出四面体间隙中氢原子的进入使轴向(110)面间距有所增加, 同时内部应力的平衡作用使轴向(200)面间距有所减少. 未充氢试样在达到 1250 MPa 抗拉强度发生颈缩塑性断裂, 而含有 8.010-6可扩散氢的试样在分步加载至 500MPa时发生脆性断. 中子衍射分析表明, 未充氢试样在拉应力加载至500 MPa时均基本符合线弹性变形, 但至700 MPa时, 轴向{200}晶粒较其余取向晶粒优先显示非线弹性变形, 至 800 MPa 时轴向{110}晶粒也出现非线弹性变形, 轴向{200}晶粒优先产生微屈服现象, 而轴向{211}晶粒仍然处于线弹性阶段; 充氢试样在拉伸至 300 MPa 时, 轴向{110}晶粒出现非线弹性变形, 至 400 MPa 时轴向{200}晶粒也出现非线弹性变形, 轴向{110}晶粒优先产生微屈服现象, 轴向{211}晶粒仍处于线弹性阶段. 断口剖面观察显未充氢试样内形成明显的轴向{110}拉伸纤维织构, 而氢脆试样内除了明显的晶界裂纹萌生, 还有晶内裂纹扩展与局部晶体转动特征. 基于不同取向晶粒的微屈服概念, 解释了充氢导致轴向{110}晶粒优先微屈服而不是轴向{200}晶粒优先微屈服, 同时以氢伴随微区塑性变形的方式发生脆性断裂.
The tensile deformation behavior and the axial lattice strain response of 1250 MPa ultra-high strength steels with and without hydrogen charging were comparably investigated using neutron diffraction together with the fracture morphology and microstructure observation. Before tensile loading, the axial (110) lattice plane spacing of hydrogen charged steel was found larger than that of non-charged specimen while the axial (200) lattice plane spacing of the former was smaller than that of the latter, suggesting that the hydrogen atoms occupied the tetrahedral site promoted the increment of axial (110) lattice plane spacing while the balanced internal stress resulted in the proper decrement of axial (200) lattice plane spacing. The necking and ductile fracture after approaching the 1250 MPa tensile strength occurred in the non-charged specimen, while the brittle fracture occurred in the 8.010-6 hydrogen charged specimen at 500 MPa holding during step-by-step loading. The neutron diffraction analysis showed that in the non-charged specimen, the linear elastic deformation was kept up to 500 MPa loading, the nonlinear elastic deformation was observed preferably on the axial (200) reflection at 700 MPa, and then on the axial (110) reflection at 800 MPa; the axial {200} grain orientation-dependent microyielding was observed preferably at 800MPa while the (211) reflection was still under linear elastic deformation. Comparably, in the hydrogen charged specimen, the nonlinear elastic deformation was observed preferably on the axial (110) reflection at 300 MPa, and then on the axial (200) reflection at 400 MPa; the axial {110} grain orientation-dependent microyielding was observed preferably at 400MPa while the axial (211) reflection was still under linear elastic deformation. The microstructure observation under fracture surface confirmed the typical <110>-oriented tensile fiber texture in the non-charged specimen while the intergranular cracks along grain boundaries, quasi-cleavage/cleavage cracks and local crystal rotation in various grains of the hydrogen charged specimen. A concept about crystallographic orientation dependent microyielding was employed here to explain the above results, i.e. the hydrogen charging promoted the axial {110} grain orientation-dependent microyielding rather than axial {200} grain orientation-dependent microyielding, and the diffusible hydrogen embrittled the matrix microstructure, accompanying with local plastic deformation.