钛合金BT9低周疲劳变形结构的研究

在室温下对钛合金BT-9单轴拉压及多轴非比例载荷的低周疲劳试验后．利用扫描电镜及透射电镜对材料的疲劳变形结构进行观测。结果表明：在单轴加载条件下,断口的形貌为韧窝。在非比例加载条件下,断口的形貌为准解理断裂和解理断裂。随着非比例载荷程度（相位角）的增大,断口的形貌由蜂窝状韧窝向河流花样的解理断裂形貌方向发展。     

Ti60钛合金室温保载疲劳性能及断裂行为

研究高峰值应力条件下Ti60钛合金双态组织和片层组织的低周疲劳与保载疲劳性能,利用金相显微镜(OM)、扫描电子显微镜(SEM)和电子背散射衍射(EBSD)等观察和分析Ti60钛合金的显微组织与疲劳断裂行为。结果表明:显微组织对低周疲劳性能影响不大,但显著影响保载疲劳性能,双态组织保载疲劳敏感性大于片层组织;保载情况下,疲劳寿命显著下降;随峰值应力的提高,疲劳寿命下降,保载疲劳敏感性增加;相同循环周次内,保载疲劳塑性应变累积大于低周疲劳,双态组织的塑性应变累积大于片层组织;低周疲劳裂纹萌生于试样表面,为单裂纹源,而保载疲劳裂纹为内部多源萌生;断口表面均存在准解理小平面,双态组织断口准解理小平面密度大于片层组织。     

Quasi-cleavage fracture planes in spheroidized A533B steel

Electron backscattered diffraction (EBSD) has been used to acquire crystal orientation information around unusual microcracks induced by tensile deformation of notched specimens of spheroidized A533B steel. This unusual fracture mode has been called quasi‐cleavage and occurs at relatively low temperatures with fracture energies below that of the upper shelf. EBSD measurements on sectioned samples showed that the quasi‐cleavage cracks were intragranular. A two‐dimensional analysis technique was used in which EBSD measured crystal orientations were combined with secondary electron imaging to obtain the trace of the crack facet on the section plane. The measurements revealed that the observed crack facets were consistent with crack propagation along the {001} and {011} planes.     

An experimental observation of dislocation nucleation based on the peierls concept

The HREM-moiré method developed by Dai and Xing [1] is an experimental technique which allows for the direct measurement of such parameters as displacement, strain and dislocation in the nanoscopic range. This technique was used to measure the nanoscopic deformation field near the tip of a quasi-cleavage crack in silicon. A process of dislocation nucleation was observed. A long dislocation extending about 600 burgers vectors was found at the crack tip and the slip distribution along it was measured. This distributed dislocation has a similar slip structure to the one based on the Peierls concept described by Rice [2], but has a much longer slip range. The nanoscopic strain distribution near the crack tip was obtained. There is a strain field controlled by linear elastic fracture mechanics at the very vicinity of the crack tip. This article based on a presentation made in the symposium “The 4th International Conference on Fracture and Strength of Solid”, held at POSTECH, Pohang, Korea, August 16–18 under the auspices of Far East and Ocean Fracture Society (FEOFS),et al.     

不锈耐热钢制件渗氮层缺陷的原因分析及其改进的工艺方法

本文分析了4Cr14N114W2Mo钢制件经一般气体氮化的渗氮层产生裂纹和剥落等缺隔的形式和主要原因。试验论证了氨氮氮化和离子氮化等工艺方法在解决渗氮层常见缺陷方面所起到的作用和取得的效果。     

Gaseous hydrogen embrittlement of T-250 laser welds

The tensile properties of laser-welded T-250 maraging steel are measured, with attention paid to the influence of strain rate and gaseous hydrogen on the fracture behavior of welded specimens. Post-weld heat treatments are performed on laser-welded specimens to obtain underaged (WU), peak-aged (WP), and overaged (WO) specimens. Hydrogen embrittlement (HE) affects the tensile fracture behavior of the welded specimens; HE changes not only the fracture mode but also the fracture location. Without the influence of hydrogen, the fracture location is at the softest region, the weld metal (WM), and the fracture appearance reveals a ductile dimple fracture. For welds sensitive to HE, the fracture is initiated at the heat-affected zone (HAZ) with coarse grain size, and the associated fracture surface exhibits intergranular and quasi-cleavage fractures that are brittle in nature. In addition, the HAZ with coarse grain size is more prone to HE, as compared to other regions in the welded specimens. The WU specimens are susceptible to HE in air under a low strain rate, while the WP specimens are only susceptible to gaseous hydrogen embrittlement (GHE). However, the WO specimens are immune to GHE and insensitive to strain rate.     

X70管线钢焊接接头热影响区的冲击性能

对X70管线钢焊接接头热影响区进行了冲击试验,对结果进行了分析。结果表明：X70管线钢焊接接头热影响区冲击试样的冲击功与断口剪切面积基本成线性比例关系,冲击功越高,剪切面积越大。焊接接头热影响区冲击试样的断口由韧性区、脆性区和韧脆混合区组成。脆性区为解理断裂,韧脆混合区为准解理断裂。     

AZ31镁合金及其TIG焊接接头断裂机理研究

对AZ31镁合金及其焊接接头进行拉伸、冲击和疲劳试验,分析了镁合金的断裂机理及疲劳裂纹扩展方向.母材拉伸试验结果表明,试样几乎没有缩颈,抗拉强度为236.29 MPa;焊接接头的抗拉强度为185.68 MPa,拉伸断裂从焊接接头焊趾部位启裂,抗拉强度为母材的78%.冲击试验在-80～340 ℃进行,结果表明,在较低温度下AZ31镁合金冲击韧性较小,断口为准解理形貌的脆性断裂;随着温度的增加,断裂形式由准解理+韧窝形貌的混合断裂过渡为韧性断裂;在常温下焊缝中心的冲击韧性比母材的高,但热影响区的冲击韧性较差.AZ31B镁合金母材的疲劳强度为66.72 MPa,对接接头的疲劳强度为39.00 MPa;母材疲劳断口由解理台阶组成,为脆性断裂;焊接接头疲劳断口由解理和准解理台阶组成,为脆性断裂.     

Hydrogen-enhanced cracking of 2205 duplex stainless steel

Tensile and fatigue crack growth tests of 2205 duplex stainless steel (DSS) were performed in laboratory air, gaseous hydrogen at 0.2 MPa and saturated H₂S solution. The longitudinal specimen showed a lesser degradation of tensile properties than the transverse ones in saturated H₂S solution. The orientation of specimens with respect to rolling direction had little influence on the fatigue crack growth rate (FCGR) of the alloy in air. Furthermore, 2205 duplex stainless steel was susceptible to hydrogen‐enhanced fatigue crack growth. Transmission electron micrographs, in addition to X‐ray diffraction, revealed that the strain‐induced austenite to martensite transformation occurred near the crack surface within a rather narrow depth. Fatigue fractography of the specimens tested in air showed mainly transgranular fatigue fracture with a small amount of flat facet fracture. Furthermore, extensive quasi‐cleavage fracture of 2205 duplex stainless steel was associated with the hydrogen‐enhanced crack growth.     

显微组织对TC11合金高温保时疲劳敏感性的影响

详细研究了等轴、三态、网三种组织对ＴＣ１１合金（Ｔｉ－６．５Ａｌ－３．５Ｍｏ－１．５Ｚｒ－０．３Ｓｉ）５２０℃高温保时疲劳敏感性的影响。结果表明,当在每次循环峰值保时３ｍｉｎ时,三种显微组织的ＴＣ１１合金均呈现疲劳寿命显著下降,其中等轴组织下降最大,三态组织其次,网篮组织最小。ＳＥＭ和ＴＥＭ观察显示,等轴和三态组织的保时敏感性是以大量准解理断裂和车辙状平面滑移为其断裂特征,且准解理断裂和平面滑移随