旋锻Mo-Ti-Zr合金棒材的退火行为

采用冷等静压、高温烧结和直接高温旋锻的方法制备Mo-Ti-Zr合金棒材,研究不同退火温度对合金力学性能与显微组织的影响以及对断面收缩率为30%的旋锻Mo-Ti-Zr合金棒材的退火行为。结果表明:当退火温度低于1000℃时,随着退火温度的升高,Mo-Ti-Zr合金硬度未急剧下降,抗拉强度和伸长率逐渐提高;经900℃退火后,合金抗拉强度达到669MPa,伸长率达到3.1%,获得良好的综合力学性能;当退火温度在800～1000℃范围内时,Mo-Ti-Zr合金晶粒发生再结晶细化;旋锻态Mo-Ti-Zr合金的断口主要为穿晶解理断裂,随着退火温度的提高,出现较多细晶粒的穿晶断裂和沿晶断裂。     

等通道转角挤压制备超细晶Mg15Al双相合金组织与性能

对高铝双相合金Mg15Al在553K以Bc路线进行了不同道次的等通道挤压(ECAP),获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm～200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32.04%,抗拉强度σb从150MPa提高到269.3MPa,延伸率δ由0.05%提高到7.4%;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。     

等通道转角挤压制备超细晶Mg15A1双相合金组织与性能

对高铝双相合金Mg15A1在553K以Bc路线进行了不同道次的等通道挤压（ECAP）,获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm-200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32．04％,抗拉强度σb从150MPa提高到269．3MPa,延伸率δ由0．05％提高到7．4％;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。     

焊后热处理对Ti-22Al-27Nb合金激光焊接接头组织与高温性能的影响

研究焊后热处理对激光焊接2.5 mm厚Ti-22Al-27Nb合金组织和高温力学性能的影响。结果表明,Ti-22Al-27Nb合金激光焊接焊缝组织为单一的B2相。焊缝650℃高温抗拉强度为母材的75%,塑性则仅为母材塑性的40%左右。拉伸断口形貌为岩石状,呈现沿晶断裂特征。经过焊后热处理,焊缝组织为B2相+O相。相对于未热处理接头,热处理后焊缝和热影响区的硬度下降很多并趋于平缓。热处理温度750℃、保温时间1 h时焊接接头650℃高温抗拉强度达到了母材的87.5%,塑性为母材的82.2%,接头断裂形式为解理断裂。     

固溶处理对差压铸造GW103K合金组织和性能的影响

通过金相显微镜、扫描电镜、X射线衍射等,分析了砂型差压铸造Mg-10Gd-3Y-Zr合金(GW103K)固溶处理后的微观组织,并进行了室温力学性能试验,对其断口形貌和断裂机理进行了探讨.结果表明,当固溶温度由500℃上升到535℃时,合金的晶粒尺寸由73μm增加到90μm,T4态合金主要由αMg固溶体+富(Gd+Y)方块相组成,经535℃×10 h处理后的合金具有最佳综合力学性能,其抗拉强度、屈服强度和伸长率分别达到231 MPa、149 MPa和4.8%;T4态合金的断裂行为主要为沿晶断裂,同时伴有少量的穿晶断裂.     

不同热处理的热连轧GH4169合金组织及抗蠕变性能研究

研究了3种不同热处理工艺下热连轧GH4169合金的组织与抗蠕变性能。结果表明,3种不同的热处理工艺对晶粒大小有一定的影响,DA态热连轧GH4169合金的组织最细小,HST态合金晶粒尺寸比ST态合金晶粒尺寸略大;δ相的含量随固溶处理时间的增加而增加,且主要在晶界处析出。在650℃/725MPa的实验条件下,DA态热连轧GH4169合金的抗蠕变性能最好,HST态合金抗蠕变性能最差。对3种不同热处理工艺的热连轧GH4169合金蠕变断裂试样的断口进行观察,其断裂方式主要表现为沿晶断裂。     

人工时效对2A12铝板力学性能和强化相的影响

在不同温度和保温时间下对2A12铝合金冷轧板进行了人工时效处理,通过显微硬度和室温拉伸实验测试了合金的力学性能,对不同时效阶段合金的微观组织和析出相进行了表征。研究发现,2A12铝合金冷轧板具有单个时效峰,时效温度越高,达到峰值时效所需的时间越短,时效温度与时间对其力学性能均具有较大影响。随时效时间的增加,合金断裂方式由韧性断裂逐渐转变为沿晶韧窝断裂和穿晶断裂。时效初期合金主要为Cu-Mg团簇强化,峰值时效时为Cu-Mg团簇和GPB区强化,过时效时析出相逐渐转化为稳定的S (Al₂CuMg)相。在考虑均质形核与非均质形核的共同作用下,2A12铝合金冷轧板的时效脱溶析出序列为过饱和固溶体(SSS)→Cu-Mg团簇+S_inhomo→Cu-Mg团簇+GPB区+S_inhomo→Cu-Mg团簇+GPB区+S_homo+S_inhomo→S。     

时效处理对铝锂合金断裂行为的影响

通过拉伸试验机、扫描电镜、透射电镜等设备对不同时效工艺下铝锂合金厚板的拉伸性能、微观组织以及断裂特征进行了系统研究。结果表明:随人工时效时间延长,合金的高向强度迅速增加,同时延伸率快速降低,合金的断裂方式也由穿晶滑移剪切+沿晶混合断口转变为单纯的沿晶断口。时效过程中晶内析出了大量的T₁相,提高了晶内强度,抑制了拉伸过程中晶内的协调变形,降低了合金的塑性并导致合金沿晶开裂。     

热锻对喷射成形7055-T6合金组织和性能的影响

以喷射成形7055-T6铝合金为对象,借助万能力学试验机、电化学工作站、光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)等手段研究热锻对挤压合金显微组织与性能的影响。结果表明:挤压合金的纵向抗拉强度为705 MPa,屈服强度为665 MPa,断口形貌表现为沿晶断裂,而锻造后合金的抗拉强度、屈服强度分别下降了33 MPa和34 MPa,但伸长率、硬度和导电率均有所上升,断口形貌表现为韧性断裂;挤压合金晶粒较均匀,组织有方向性,但热锻后合金部分晶粒长大合并,部分晶粒破碎;合金晶界析出相中的主要元素含量均比基体高,且热锻后合金晶界析出相中的Mg、Zn元素含量降低,Cu元素含量升高;合金经峰值时效后,晶内GP区和η′析出相为主,晶界析出相近似连续分布,导致合金耐蚀性不好;锻造后晶界和晶内析出相均长大粗化,使得合金强度下降,耐蚀性提高。     

喷射成形Al-Zn-Mg-Cu合金热处理工艺与力学性能

利用喷射成形技术制备了超高强Al12Zn2.4Mg1.1Cu合金.对合金进行热挤压,在不同固溶温度和时间下对挤压合金进行固溶处理,并进行力学性能测试.结果表明,挤压态合金存在着大量的第二相颗粒,为MgZn2相和富铜相,合金微观组织中包括微米级晶粒和纳米级晶粒.合金进行T6热处理后,抗拉强度为749.6 MPa,延伸率为10.9%,拉伸试样的断口分析表明,合金的断裂方式主要为穿晶断裂.     

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.     

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。     

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。     

纯剪载荷作用下的岩石断裂

利用四点弯剪切法研究了岩石纯剪载荷作用下的断裂规律，并提出了岩石发生真Ⅱ型断裂的条件，探讨了测定岩石真Ⅱ型断裂韧性的方法。     

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.     

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.     

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.     

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。     

THEORETICAL AND EXPERIMENTAL STUDIES ON FRACTURE PLANE CONTROL BLAST WITH NOTCHED BOREHOLES

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