Significant influence of sharp grain boundary corner on tensile elongation of copper bars with columnar grains and its mechanism

The reason why elongation of copper bars with columnar grains drops significantly after small cold-drawing was explored. The copper bars were prepared by warm-mould continuous casting. Tensile test was interrupted at various tensile strains in order to detect crack origin. Electron backscattered diffraction（EBSD） was used to analyze dislocation slip bands. It is found that the as-cast microstructure contains sharp grain boundary（GB） corners nearly parallel to the solidification direction（SD）. Elongation of the copper bars drops significantly from 68.8% in as-cast state to 18.8% in as-drawn state. It is revealed that plastic deformation becomes severer in the vicinity of sharp GB corners. Locally accumulated internal stress even activates a slip system with very low Schmid factor of 0.17. The localized plastic deformation near sharp grain boundary corner promotes crack initiation and propagation, which eventually leads to the significant drop of elongation.

Mesh generation and optimization from digital rock fractures based on neural style transfer

The complex geometric features of subsurface fractures at different scales makes mesh generation challenging and/or expensive.In this paper,we make use of neural style transfer(NST),a machine learning technique,to generate mesh from rock fracture images.In this new approach,we use digital rock fractures at multiple scales that represent’content’and define uniformly shaped and sized triangles to represent’style’.The 19-layer convolutional neural network(CNN)learns the content from the rock image,including lower-level features(such as edges and corners)and higher-level features(such as rock,fractures,or other mineral fillings),and learns the style from the triangular grids.By optimizing the cost function to achieve approximation to represent both the content and the style,numerical meshes can be generated and optimized.We utilize the NST to generate meshes for rough fractures with asperities formed in rock,a network of fractures embedded in rock,and a sand aggregate with multiple grains.Based on the examples,we show that this new NST technique can make mesh generation and optimization much more efficient by achieving a good balance between the density of the mesh and the presentation of the geometric features.Finally,we discuss future applications of this approach and perspectives of applying machine learning to bridge the gaps between numerical modeling and experiments.

超深井用160钢级超高强度高韧性套管的研制及组织表征

根据超深井开发要求对超高强度高韧性套管的合金化技术和制造工艺进行研究,开发出具有优异韧性和抗延迟断裂性能的BG160V超高强度高韧性套管,并分析了该BG160V套管在不同服役温度下的强韧性以及微观组织。工业性试制的性能检测结果表明:该套管的屈服强度达到1100 MPa以上,0℃横向夏比冲击功超过名义屈服强度的10%,满足超深井油气资源开发对套管性能的要求;管体晶粒度达到11级,平均有效晶粒尺寸2.45μm,细小的晶粒是材料具有良好韧性和抗延迟断裂性能的主要保证。

电厂汽轮机主汽门螺栓断裂原因

某电厂主汽门用GH6783合金紧固螺栓在回装热紧过程中发生断裂。采用宏观观察、化学成分分析、扫描电镜及能谱分析、金相检验、力学性能测试等方法对螺栓断裂的原因进行分析。结果表明:螺栓由中心孔内表面向外扩展断裂,呈晶界氧化脆性断裂特征;β时效处理不当使晶界处未生成网状较窄且连续的β-NiAl相,导致晶界的抗氧化性较差;在螺栓紧固过程中,外加应力高于晶界强度,最终导致螺栓断裂。

梯度晶粒结构材料拉伸断裂行为的晶体塑性有限元模拟

梯度晶粒结构材料通过在材料内部构筑由纳米晶、细晶渐进过渡至粗晶的微结构,使其展现出诸多优异的力学性能,如高强度、高韧性和抗疲劳性等.工程材料在长期服役过程中,不可避免会发生疲劳和断裂,严重威胁材料的服役安全和使用寿命.相关实验研究报道了纳米晶材料具有沿晶断裂的特点,且抗断裂性能与晶粒尺寸相关,然而梯度晶粒结构材料具有复杂的晶粒尺寸分布,其断裂机理仍需进一步揭示.为此,基于晶体塑性有限元方法,将Cohesive单元植入有限元模型的多晶晶界处,分别模拟了均匀晶粒结构铜和梯度晶粒结构铜的单拉力学性能,并研究了预制裂纹对梯度晶粒结构材料裂纹扩展的影响.结果表明,所提出的晶体塑性本构模型结合晶界损伤机制可以有效模拟梯度晶粒结构材料的塑性变形以及裂纹扩展过程.在单轴拉伸变形下,梯度晶粒结构材料展现了应力与塑性应变的梯度分布特征.一方面,由于晶粒尺寸效应,尽管基体细晶区具有相对较低的流动应力,但是表层纳米晶强度高.此外,由于应变硬化能力的不同,尽管纳米晶区域表现出较低的塑性应变,但细晶区域呈现较高的塑性变形能力.因此,梯度晶粒结构通过强度与应变硬化能力的差异,有效地优化了强度与韧性的协同作用,从而增强了抵抗裂纹扩展的能力.纳米晶区域预制裂纹对梯度晶粒结构材料的强度影响较大,因此抑制纳米晶区域的裂纹萌生有助于晶粒结构材料的安全服役.

Modeling the Interaction between Vacancies and Grain Boundaries during Ductile Fracture

The experimental results in previous studies have indicated that during the ductile fracture of pure metals,vacancies aggregate and form voids at grain boundaries.However,the physical mechanism underlying this phenomenon remains not fully understood.This study derives the equilibrium distribution of vacancies analytically by following thermodynamics and the micromechanics of crystal defects.This derivation suggests that vacancies cluster in regions under hydrostatic compression to minimize the elastic strain energy.Subsequently,a finite element model is developed for examining more general scenarios of interaction between vacancies and grain boundaries.This model is first verified and validated through comparison with some available analytical solutions,demonstrating consistency between finite element simulation results and analytical solutions within a specified numerical accuracy.A systematic numerical study is then conducted to investigate the mechanism that might govern the micromechanical interaction between grain boundaries and the profuse vacancies typically generated during plastic deformation.The simulation results indicate that the reduction in total elastic strain energy can indeed drive vacancies toward grain boundaries,potentially facilitating void nucleation in ductile fracture.

万米井用超高强高韧套管的研制及组织表征

根据万米特深井超高温超高压工况需求,开展超高强高韧套管合金化技术和制造工艺研究,开发出具有良好韧性、高温强度、抗挤毁和抗延迟断裂性能的BG155V超高强高韧套管,批量试制的性能检测结果表明屈服强度达到1100 MPa以上,0℃横向夏比冲击功平均值达到名义屈服强度的10%。对套管不同服役温度下强度、低温韧性以及微观组织进行了分析,发现采用热轧后控制冷却工艺的管体晶粒度达到11级,通过细小的晶粒保证材料良好韧性和抗延迟断裂性能,提升了万米特深井油气资源开发用套管安全服役的可靠性。

EH36厚壁海上风电用钢及其焊接热影响区的断裂韧性研究

目的开发大壁厚抗断裂、耐不同线能量焊接EH36海上风电用钢,满足深水海上风电平台的服役需求。方法试制了80 mm厚的EH36海上风电用钢,研究了不同温度下EH36的断裂韧性变化规律,并进行了7 kJ/cm和50 kJ/cm线能量的焊接试验。通过裂纹尖端张开位移(CTOD)试验,评估母材及焊接CGHAZ的断裂韧性。使用光学显微镜和电子显微镜对其微观组织及其CTOD试样断口形貌进行表征和分析。结果EH36的断裂韧性在−10~−30℃区间内保持较高的值,−40℃为该材料的韧脆转变温度,此时断裂模式从韧性断裂转变为脆性断裂,但其临界CTOD平均值仍高于标准要求。此外,7 kJ/cm热输入的CGHAZ临界CTOD平均值为0.658 mm,其微观组织主要由针状铁素体组成,50 kJ/cm热输入的CGHAZ临界CTOD平均值为0.468 mm,其微观组织主要由针状铁素体和粒状贝氏体组成。在电镜下观察到CGHAZ内含有大量由Ti的氧化物组成的高熔点夹杂物,大量针状铁素体在其周围形核并生长,可有效提升CGHAZ的断裂韧性。结论所开发的EH36厚壁海上风电用钢具有优越的抗断裂性能和焊接性能。

Characteristic stress variation and microcrack evolution of granite subjected to uniaxial compression using acoustic emission methods

The size of mineral grain has a significant impact on the initiation and propagation of microcracks within rocks.In this study,fine-,medium-,and coarse-grained granites were used to investigate microcrack evolution and characteristic stress under uniaxial compression using the acoustic emission(AE),digital image correlation(DIC),and nuclear magnetic resonance(NMR)measurements.The experimental results show that the characteristic stress of each granite decreased considerably with increasing grain sizes.The inflection points of the b-value occurred earlier with an increase in grain sizes,indicating that the larger grains promote the generation and propagation of microcracks.The distribution characteristics of the average frequency(AF)and the ratio of rise time to amplitude(RA)indicate that the proportion of shear microcracks increases with increasing grain size.The NMR results indicate that the porosity and the proportion of large pores increased with increasing grain size,which may intensify the microcrack evolution.Moreover,analysis of the DIC and AE event rates suggests that the high-displacement regions could serve as a criterion for the degree of microcrack propagation.The study found that granites with larger grains had a higher proportion of high-displacement regions,which can lead to larger-scale cracking or even spalling.These findings are not only beneficial to understand the pattern of microcrack evolution with different grain sizes,but also provide guidance for rock monitoring and instability assessment.

船用高止裂韧度特厚钢板EH47BCA工业研发

介绍了集装箱船用高止裂韧度特厚钢板EH47BCA的工业化研发。研发结果表明:采用NEU⁃Rolling往复相变控轧工艺能够更好地实现组织调控,与传统TMCP工艺比较,在全厚度的大角度晶界比例更高,组织更加细小均匀,表现出优异的低温韧性。研发的100 mm厚高止裂韧性EH47BCA钢在全尺寸拉伸断裂时表现出显著阻滞脆性裂纹传播的能力,形成了“多峰”分布的宏观断口,提高了钢板全厚度断裂时的止裂韧性,−10℃止裂韧性达到9041 N/mm^(3/2)。

微晶铸造对K4169合金组织及持久性能的影响

分别采用普通铸造、细晶铸造和微晶铸造工艺制得了晶粒度为ASTM M9~M7级、ASTM M14~M9级和ASTM 3~5级的K4169合金试样,研究了微晶铸造对K4169合金组织及持久性能的影响。研究结果表明,微晶铸造工艺可显著细化晶粒,降低凝固偏析,减少Laves相和大块MC碳化物,增加γ″相体积分数;使合金704℃/448 MPa条件下的持久性能相比于普通铸造和细晶铸造合金分别提高了621%和44%,达到614.9 h;断裂模式从普通铸造K4169的脆性穿晶断裂转变为微晶铸造K4169的韧性沿晶穿晶混合型断裂。微晶铸造工艺引起的晶粒细化和γ″相体积分数的提高,有效强化了K4169合金,而大块MC碳化物及Laves相的减少,减少了潜在的裂纹萌生、扩展位置,二者共同作用提高了K4169合金的持久寿命,并降低了性能数据分散性。微晶铸造工艺可获得良好的综合力学性能,提升K4169合金机匣、壳体、扩压器等整体结构件在700℃以下的服役性能,有良好的应用前景。

自支撑金刚石厚膜三方向三点弯曲断裂韧性对比研究

采用直流电弧等离子体喷射和微波等离子体化学气相沉积法制备了三片直径为125 mm、厚度大于1 mm的自支撑金刚石膜。通过SEM、XRD、Raman、CT等检测手段对样品进行了形貌、物相表征,进一步通过激光预制裂纹方法研究了缺陷和晶粒尺寸对生长面、形核面及侧面三个方向断裂韧性的影响。结果表明,在金刚石薄膜沉积过程中,许多缺陷(包括孔隙)被引入薄膜中,特别是较厚膜中靠近生长面一侧的孔隙尺寸可以达到微米级,这会影响不同方向载荷下的断裂韧性。由于近生长面的晶粒尺寸最小,自支撑金刚石膜在生长面形成的裂纹具有最大断裂韧性,分别为7.8、8.3和9.2 MPa·m^(1/2)。对于较薄的样品,侧面裂纹的断裂韧性介于生长面和形核面之间,这与晶粒尺寸关系一致,表明断裂韧性受晶粒尺寸的影响。然而,当厚度超过0.8 mm时,生长侧附近的孔隙数量会增加,导致较厚的金刚石薄膜的断裂韧性最小(5.4 MPa·m^(1/2))。本研究为金刚石上施加载荷方向的选择提供了指导。

晶粒尺寸对Inconel 718薄板塑性微变形行为的影响:实验与建模

随着航空航天工业的迅速发展,对微型化Inconel 718薄板构件的需求越来越大。然而,晶粒尺寸显著影响金属薄板的塑性变形行为,在很大程度上限制了Inconel 718薄板构件的生产和应用。本文对不同晶粒尺寸的Inconel 718薄板进行了一系列单轴拉伸试验和扫描电镜实验,研究了晶粒尺寸对其塑性变形行为的影响。通过EBSD技术表征了晶粒尺寸、晶粒取向和晶粒平均取向偏差,阐明了晶粒尺寸效应的变形机制。研究结果表明,随着晶粒尺寸的增大,在拉伸应力作用下,晶粒旋转和协调变形机制减弱,取向转变为<232>的晶粒数量逐渐减少,从而导致屈服强度和最大抗拉强度显著降低;此外,随着晶粒尺寸的增大,晶粒内部的塑性变形明显减弱,晶界滑动逐渐成为拉伸过程中主要的变形机制,导致断裂应变减小,韧性断裂特征减弱。本文综合考虑晶粒尺寸和应变量影响,建立了能够应用于Inconel 718薄板的微成形研究的混合材料本构模型。

塔式起重机用高强度螺栓断裂原因

某塔式起重机用35CrMoA钢高强度螺栓在服役过程中发生断裂现象,采用螺栓头下圆角半径测量、化学成分分析、力学性能测试、低倍检验、断口分析、金相检验等方法研究了螺栓断裂的原因。结果表明:螺栓在服役过程中发生松动后未及时将其拧紧,在螺栓局部产生应力集中并形成疲劳源,导致螺栓疲劳断裂。

550 MPa级微合金化高强结构钢设计与生产

介绍了屈服强度550 MPa级微合金化高强钢在中板坯连铸-连轧生产线上的设计开发与生产实践情况。3种实验方案对比结果显示:高锰低铌钛体系采用低温卷取,晶粒度11级,屈服强度668 MPa,碳化物弥散析出,冲击断口呈现明显的混合断裂形貌,聚集韧窝和准解理断裂交叉分布,冲击吸收功较低。中锰、中铌、高钛成分体系采用高温轧制和卷取,晶粒度10级,屈服强度649 MPa,碳化物在晶界析出充分,提升了韧性,但是强度降低明显;降低卷取温度后,组织细化显著,晶粒度增加至12级,屈服强度721 MPa,但纵向组织出现粗化的条状铁素体,材料组织均匀性变差;高温卷取冲击试样断口基本为韧窝形貌,而低温卷取的试样断口韧窝小且浅,且有少量解理断口。低锰、高铌、中钛成分体系下,晶粒度11级,屈服强度620 MPa,碳化物弥散析出效果最好,珠光体含量少且尺寸均匀、细小;冲击试样断口也呈现显著韧性断裂形貌,部分位置韧窝大且深,呈现微孔聚集断裂的典型形貌,但仍可观察到少量解理撕裂的形貌。试制结果表明:通过添加Nb、Ti等强化元素,可优化材料组织组成、尺寸和均匀性,实现550 MPa级产品材料强度和塑韧性最佳匹配。

变速器输出轴断裂失效分析

某车型综合耐久试验过程中变速器输出轴发生断裂。通过化学成分检测、显微组织观察、断口形貌及能谱分析等方法,对由20CrMnTi制成的变速器输出轴断裂原因进行分析。结果表明,原材料熔铸凝固过程中铬(Cr)、锰(Mn)元素扩散速率较慢在枝晶间汇集,晶间液相区溶质元素在晶界造成元素偏析,从而析出Cr、Mn化合物使晶界弱化,在后续热处理工艺产生内应力和相变应力的综合作用下,弱化的晶界上产生微裂纹。当承受交变载荷时,微裂纹沿原奥氏体晶界逐步向内扩展,最终导致零部件断裂。工程使用端可借鉴文章介绍的失效分析方向,控制使用端此类失效问题的发生。

气瓶阀阀体断裂原因分析

针对一起气瓶阀阀体断裂造成气瓶阀失效的案例,对气瓶阀阀体进行宏观检查、化学成分分析、名义Zn含量计算、显微组织分析、显微硬度分析、断口微观分析。结果表明:气瓶阀阀体断裂主要与显微组织中Pb相颗粒在晶界聚集及阀体内部结构产生的应力集中有关。Pb相颗粒在晶界聚集,引起晶界弱化,裂纹在晶界上萌生;阀体内部的应力集中加速了裂纹扩展。最终在气瓶阀多次使用后,气瓶阀阀体发生断裂。

山西义兴寨金矿床金矿物颗粒的产出及其成矿动力学意义

山西义兴寨金矿床的金主要呈包体金和裂隙金两种产出状态。文章根据成矿地球化学动力学理论 ,论证了金元素在含矿断裂发生脆性破裂和脆_韧性扩张活动中析出的化学反应类型 ,以及受反应动力学条件的制约 ,形成矿石中金不同产出状态的规律。指出热液矿床中普遍存在的包体金为热液成矿早期阶段断裂发生脆性破裂和成矿流体沸腾 ,导致快速反应结晶的产物 ;而裂隙金和晶隙金为成矿晚期金等矿质在流体中残余富集 ,同时成矿断裂再次发生脉动破裂 ,即成矿热力学演化与有利的构造动力学因素耦合作用的结果。

Effects of Al-Ti-B-RE grain refiner on microstructure and mechanical properties of Al-7.0Si-0.55Mg alloy

To investigate the effects of Al-Ti-B-RE grain refiner on microstructure and mechanical properties of Al-7.0Si-0.55Mg （A357） alloy, some novel Al-7.0Si-0.55Mg alloys added with different amount of Al-STi-1B-RE grain refiner with different RE composition were prepared by vacuum-melting. The microstructure and fracture behavior of the AI-7.0Si-0.55Mg alloys with the grain refiners were observed by X-ray diffraction （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM）, and the mechanical properties of the alloys were tested in mechanical testing machine at room temperature. The observation of AI-Ti-B-RE morphology and internal structure of the particles reveals that it exhibits a TiAl3/Ti2Al20RE core-shell structure via heterogeneous TiB2 nuclei. The tensile strength of Al-7.0Si-0.55Mg alloys with Al-5Ti-1B-3.0RE grain refiner reaches the peak value at the same addition （0.2%） of grain refiner.

长柱状晶高韧性氧化铝陶瓷的制备与性能研究

针对一般氧化铝陶瓷材料断裂韧性差的缺点 ,通过球磨的方法向初始原料氢氧化铝中添加晶种 ,并采用热压烧结方式 ,使氧化铝生长成长柱状晶粒结构 ,产生了明显的增韧效果 ,使这种氧化铝瓷体的断裂韧性比一般氧化铝陶瓷材料提高一倍以上 ,可达到 6 .70 MPa· m1 /2。对几种不同烧结温度下烧结的瓷体进行了显微结构分析和力学性能测试 。