Cr、Yb合金化对Al-Zn-Mg-Cu-Zr合金组织和断裂特征的影响

研究复合添加微量Cr、Yb、Zr对Al-Zn-Mg-Cu合金的显微组织和断裂特征的影响,分析其对合金韧化的作用机制.结果表明:在Al-Zn-Mg-Cu合金中复合添加Cr、Yb、Zr形成了含Cr、Yb、Zr的球形弥散相,这些均匀分布于基体上的弥散相能强烈钉扎位错和亚晶界,使基体保持形变回复组织,保持小角度晶界,抑制基体再结晶;T6态断裂机制主要为韧窝型穿晶断裂,与仅添加Zr相比,沿晶断裂抗力显著提高;晶界的无沉淀区(PFZs)较宽,且析出相在晶界呈明显不连续分布.     

淬火速率对7136铝合金应力腐蚀开裂敏感性的影响

针对7xxx系铝合金的抗应力腐蚀性能对淬火速率敏感的问题,通过浸入式末端淬火和慢应变速率拉伸实验研究了淬火速率对7136铝合金应力腐蚀开裂(SCC)敏感性的影响规律。结果显示,随着淬火速率的减小,合金的SCC敏感性先增高后降低,淬火速率约为5.3℃/s时的SCC敏感性最高;SCC裂纹扩展方式由穿晶扩展转变为沿晶扩展。淬火速率越小淬火析出相越多,尺寸越大,晶界和亚晶界附近的无沉淀析出带越宽。淬火速率大于5.3℃/s时,晶界析出相中Zn、Mg元素含量随淬火速率减小迅速增加,而淬火速率小于5.3℃/s后,Cu元素含量迅速增加。晶界和亚晶界析出相形貌特征以及晶界析出相化学成分的变化是SCC敏感性随淬火速率减小先增加后降低的主要原因。     

回火温度对42CrMo高强钢应力腐蚀断裂行为的影响

研究了回火温度对高强度42CrMo 钢应力腐蚀断裂行为的影响。结果表明,在淬火态和低温回火态.均为沿晶断裂.K_(ISCC)很低;当回火温度高于300℃后,K_(ISSCC)随回火温度升高而显著早升,断裂方式从沿晶型过渡为穿晶韧窝和沿晶的混合型。俄歇能谱和电镜分析表明,该钢的应力腐蚀断裂行为主要决定于碳比物的分布。在淬火态和低温回火态,碳化物主要分布于原奥氏体晶界,导致沿晶断裂和 K_(ISCC)值很低。较高温度回火后,晶界上碳化物的聚集粗化和晶粒内部碳化物的大量析出,导致了断裂方式由沿晶型向混合型转化和 K_(ISCC)的明显升高。     

时效制度对Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr合金断裂行为的影响

通过拉伸性能测试及金相显微镜、扫描电镜和透射电镜分析对比研究了Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr合金在T6与T74热处理状态下的力学性能、断裂行为和显微组织。结果表明:相对T6态,Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr合金经T74处理后,强度降低了约15%,但延伸率和电导率分别增加了52%和29%。合金T6态的断裂方式为穿晶剪切和沿晶韧窝混合型断裂;经过T74处理的合金断裂方式为穿晶韧窝型断裂。不同热处理状态下,晶内和晶界组织对位错运动的共同作用是决定合金断裂行为的主要原因。     

淬火转移时间对7055铝合金抗晶间腐蚀能力的影响

采用光学显微镜和透射电镜等分析技术研究了淬火转移时间对含Zr和无Zr的7055铝合金晶间腐蚀抗力的影响.结果表明,随着淬火转移时间的延长,合金的晶间腐蚀深度增加,合金的晶间腐蚀抗力降低.含Zr合金较无Zr合金具有更好的抗晶间腐蚀能力.据组织观察认为淬火转移时间延长致使晶界无沉淀析出带宽化是合金晶间腐蚀抗力下降的主要原因,Zr的添加阻碍再结晶从而提高合金的抗晶间腐蚀能力.     

真空处理和Ti含量对Mo-0.1Zr合金性能与显微

将粉末高能球磨,经压制、预烧、高温烧结和真空处理,制备Mo-0.1Zr(质量分数,下同)和含有不同Ti含量的Mo-0.1Zr-nTi(n分别为0.4,0.55,0.7,0.9)合金。研究真空处理和Ti含量对Mo-0.1Zr合金性能和组织结构的影响。结果表明,真空处理能够使Mo-0.1Zr合金的性能大大提高,尤其使合金的延伸率达到25.6%,达到甚至超过了锻造态合金的延伸率,合金的断口也由真空处理前的沿晶断裂特征转变为明显的穿晶断裂。Ti的添加,使Mo-0.1Zr合金生成了(Mo,Ti)xOy第二相粒子,第二相粒子存在于晶界之间,并随着Ti添加量的增加而增加,从而使合金的力学性能随Ti添加量的增加而下降。     

预形变和时效Al-2.73Li合金的断裂机制SCIEI

本文研究了预先冷形变对Al-2.73Li合金的机械性能和断裂行为的影响。试验结果表明,预先冷形变使合金的加工硬化率和强度提高,相应损失部分塑性。预先冷形变造成不均匀分布的胞状位错结构及晶界无沉淀带加工硬化,乃是导致塑性下降的主要原因。合金的断裂方式为沿晶和穿晶混合型。预形变后时效使沿晶断裂倾向增大。最后探讨了其断裂机制。     

喷射沉积Al－3．8Li－0．8Mg－0．4Cu－0．13Zr合金的拉伸断裂行为

采用新型的喷射沉积工艺制备了Ａｌ－３．８Ｌｉ－０．８Ｍｇ－０．４Ｃｕ－０．１３Ｚｒ合金，对合金的拉伸性能及断裂行为进行了研究，实验结果表明，喷射沉积Ａｌ－Ｌｉ合金经１９０℃，１０ｈ时效后达到峰时效状态，此时材料的综合性能最优（ＵＴＳ为５３４ＭＰａ，０．２ＹＳ为４８０ＭＰａ，延伸率为１０％）．固溶淬火态实验合金拉伸断口为完全穿晶韧窝型。时效态合金的断裂方式为穿晶和沿晶混合型实验合金沿晶断裂的主要原因是晶界无析出区和晶界平衡相的析出。     

热变形温度和淬火速率对7085铝合金组织和性能的影响

采用力学性能测试、光学显微镜、扫描电镜和透射电镜,研究热变形温度和淬火速率对7085铝合金组织和力学性能的影响。结果表明:随着热变形温度降低,再结晶体积分数显著增加,合金的力学性能先提高后降低;随着淬火速率的降低,晶界析出相粗化,晶界无沉淀析出带宽化,合金的力学性能降低。合金热变形温度越低,其淬火敏感性越高,这是由于在缓慢冷却的过程中,再结晶引起的大角度晶界和非共格的Al3Zr粒子成为MgZn2相的有利形核位置,降低合金的时效强化效应。     

7050铝合金的TTP曲线

通过分级淬火方法获得7050铝合金的时间-温度-性能(TTP)曲线.结果表明:合金TTP曲线的鼻尖温度为330 ℃,淬火敏感温度区间为240～420 ℃;等温保温时,过饱和固溶体分解析出第二相粒子,在330 ℃附近,第二相(主要为η平衡相)的析出速率达到最高;随着时间的延长,晶内η相数量增加、尺寸变大,时效后粒子周围出现无沉淀析出区,导致强化效果显著降低;晶界处η相粒子粗化,由不连续分布形貌转变为连续分布形貌,无沉淀析出带宽化;鼻尖温度的高相变驱动力和较快的扩散速率是η相析出和长大的主要原因,建议在淬火敏感区间应加快淬火冷却速率避免平衡相的析出,而高于淬火敏感区间温度时可适当降低冷却速率减小热应力的影响.     

Critical level of intergranular fracture to affect the toughness of embrittled 2.25Cr-1Mo steels

In general, the low-temperature brittle fracture mode of unembrittled ferritic steel is transgranular cleavage. During temper embrittlement, impurity elements, such as sulfur (S), phosphorus (P), antimony (Sb), arsenic (As), and tin (Sn), segregate to prior austenite grain boundaries, which results in a decrease in the grain boundary cohesive strength. As a result, the brittle transgranular cleavage fracture mode changes to intergranular decohesion in association with the decrease in the critical fracture (stress (σ _F) as well as the fracture toughness (K). However, the appearance of intergranular facets on the fracture surface does not cause a decrease in the K and σ _F values. In this work, quenched and fully tempered 2.25Cr-1Mo steel (in an unembrittled condition that exhibits almost 100% brittle transgranular cleavage fracture) has been embrittled for 24, 96, and 210 h at 520 °C to produce different proportions of intergranular fracture. These unembrittled and embrittled steel specimens were tested to measure K (at −120 and −196 °C) and σ _F (at −196 °C). The experimental results and detailed fractographic observations show that the K and σ _F values decrease with an increase in the area fraction of intergranular fracture, provided that the area fraction of the intergranular facet on the brittle fracture surface exceeded a certain critical level, approximately 20–22%.     

基于延性准则的DP800小圆角拉弯成形开裂判据

针对传统FLC无法准确预测超高强度双相钢薄板在较小凸模圆角下拉弯成形时的剪切开裂问题,采用基于延性准则的成形判据计算其应力-应变失效积分因子,结果表明,使用Brozzo和Oyane延性准则计算的失效积分因子在凸模圆角处超过失效单位值,与试验相符,说明Brozzo、Oyan延性准则能够实现小圆角半径下双相钢板材在拉弯成形中的开裂预测。     

Low-temperature fracture toughness of a heat-treated mild steel

Specimens from a 0.14 % C mild steel were austenitized at 1000 °C for 1 h and thereafter furnace-cooled or isothermally transformed at 700 °C for 0.5,2, and 8 h. The microconstituents present in the as-received material were ferrite and pearlite and their amounts did not substantially change even after heat treatment. The impact energy of the as-received and the furnace-cooled materials increased from 4 to 89 J and from 4 to 108 J, respectively, when the temperature was changed from - 196 to 23 °C. For these materials, the failure mode was by ductile fracture at 0 and 23 °C and by quasicleavage fracture at - 196 and - 40 °C. The fracture toughness did not show any significant change with isothermal transformation time at 700 °C. The failure mode of the isothermally transformed materials was always by quasicleavage fracture.     

钢丝杯锥状断口断裂机理

用金相和扫描电镜分析了钢丝杯锥状断口。结果表明,钢丝杯锥状断口形成机理主要是由于钢丝组织中存在夹杂物、组织疏松、碳偏析以及拉拔工艺不当,导致心部出现"V"型裂纹,沿"V"型裂纹断裂后形成杯锥状断口。     

Study on fracture behavior of SiCp/A356 composites

The fracture behavior of SiCp/A356 composite at room and high temperatures was studied.Under tensile stress condition at room temperature, the fracture is mostly a combination of the brittle fracture of SiC particles and ductile fracture of A356 matrix.As the tensile temperature increases, the composite changes the main fracture behavior to the separation fracture of the bonding surface between SiC particles and A356 matrix.When the tensile temperature reaches 573 K, the fracture behavior of the composites is almost the whole separation fracture of the bonding surface, which is the main strengthening mechanism at high temperature.Under the cycle stress condition at room and high temperatures, the main fracture behavior of the composites is always a combination of the brittle fracture of SiC particles and ductile fracture of A356 matrix.However, under the cycle stress at high temperature, cycle behavior of the composites changes from cycle hardening at room temperature to the cycle softening at high temperature.     

AZ31B镁合金点焊接头拉剪断裂特征

针对板厚2 mmAZ31B镁合金板材在DZ-3×100三相次级整流点焊机上进行焊接.通过对其焊接接头的拉剪试验、金相显微观察、断口SEM分析、XRD分析,研究了镁合金点焊接头拉剪断裂特征.结果表明,点焊接头拉剪断裂呈现拉剪撕裂和整核断裂两种断裂形式.熔核处断口为韧性-脆性混合型断裂,母材断口处呈现一典型的韧性断裂特征.熔核与母材的物相基本一致.母材焊后,晶界及晶面上析出硬而脆的Mg17Al12金属间化合物,且所占比例远远超过母材基体,熔核区域的断裂倾向增大,Mg17Al12金属间化合物在XRD图谱上衍射峰强.     

Micromechanism of Cleavage Fracture of Weld MetalsEI北大核心CSCD

Cleavage fracture is the most dangerous form of fracture. Cleavage fracture usually happens well before general yielding at low nominal fracture stress and strain. Cleavage fracture is often spurred by low temperature and determines the toughness in the lower shelf temperature region. This paper describes a new framework for the micromechanism of cleavage fracture of high strength low alloy (HSLA) steel weld metals. Cleavage fracture not only determines the impact toughness in the lower shelf but also plays a decisive role on the impact toughness in the transition temperature region. The toughness is determined by the extending length of a preceding fibrous crack which is terminated by cleavage fracture. Three non-stop successive stages, i.e. crack nucleation, propagation of a second phase particle-sized crack across the particle/grain boundary, propagation of a grain-sized crack across the grain/grain boundary are explained. The "critical event" of cleavage fracture is emphasized which offers the greatest difficulty during crack formation and controls the cleavage process. The critical event indicates the weakest microstructural component and its critical size which specifies the local cleavage fracture stress sigma(f) for cleavage fracture. In toughness-study it is paramount important to reveal the critical events for various test specimens. Three criteria for crack nucleation, for preventing crack nucleus from blunting and for crack propagation are testified. An active region specified by these criteria is suggested where the combined stress and strain are sufficient to trigger the cleavage fracture. It can be used in statistical analyses. A case study, using the new framework of micromechanism for analyzing toughness of 8% Ni steel welding metals is presented to analyze the experimental results.     

灭火器爆炸事故分析

某型号干粉灭火器在充填作业中发生爆炸事故。综合分析事故现场，并利用裂纹分析、断口分析、材料分析及力学分析表明：该灭火器材料合格，充填作业正常，爆炸的原因在于灭火器存在较严重的加工工艺缺陷，在筒体底部的不正常环向旋压损伤致使该部位局部厚度仅为其他部位的50％，并形成环状尖缺口缺陷，造成应力集中，局部高应力导致了低应力爆炸事故的发生。     

岩石Ⅱ型断裂韧度的实验方法

针对纯剪断裂试件存在的问题,提出了采用压剪试件实现岩石Ⅱ型裂纹剪切断裂并测试岩石剪切断裂韧度的实验方法,并通过对压剪试件的应力分布和测试结果的分析讨论,提出了岩石Ⅱ型断裂韧度实验的最佳方案,并进而讨论了Ⅱ型裂纹的两种不同断裂型式和断裂判据。     

燃气机涡轮连接螺栓断裂原因分析

某燃气轮机涡轮系统用连接螺栓,试车分解检查时发现多件断裂。采用断口宏微观观察,金相组织分析,能谱分析,故障模拟验证试验等方法,对螺栓的断裂原因进行了综合分析。结果表明:失效螺栓属于沿晶脆性断裂;螺栓装配过程中使用的高温丝扣脂中的低熔点元素Pb,在一定的拉应力、温度作用下,引起晶界腐蚀损伤是导致螺栓断裂的主要原因。该研究结果对此类螺栓的使用和故障预防可提供借鉴。