氧化法显示钢的奥氏体晶粒度的准确性

选用不同钢种在不同加热温度条件下,采用比较法和截点法对两种常用的奥氏体晶粒度显示方法,即氧化法和晶粒边界腐蚀法进行了对比性研究。结果表明：氧化法显示钢的奥氏体晶粒度的准确性能够满足生产检验的要求,氧化法与晶粒边界腐蚀法所显示的奥氏体晶粒平均弦长的差值会受钢种及加热温度的影响。     

一种适用于GH4169镍基合金奥氏体晶粒度评级的浸蚀方法

采用传统浸蚀液对GH4169镍基合金进行浸蚀,可显示包括孪晶在内的奥氏体组织,但孪晶的存在加大了奥氏体晶粒度的评级难度。通过调整浸蚀液成分,提出了一种只显示奥氏体晶界的浸蚀方法。试验结果表明:采用高锰酸钾水溶液(1.5～2g KMnO4+7～10mL H2SO4+90～110mL H2O+0.1～0.3mL HCl),水浴加热至95℃对GH4169镍基合金进行浸蚀,可清晰地显示出奥氏体晶界,而不显示晶粒内孪晶,获得的显微组织可用来准确评定合金的晶粒度级别。     

直线截点法测定金属平均晶粒度的不确定度评定

采用直线截点法对某金属晶粒的平均截距进行了测量,并对测量过程中的每个不确定度分量进行了评定,然后根据不确定度传播规律求出了平均晶粒度的合成标准不确定度,并最终给出了扩展不确定度。结果表明:在该试验条件下,试验金属平均晶粒度测定的扩展不确定度U=0.1,包含因子k=2,平均晶粒度级别数G=8.4±0.1;该次评定测量不确定度较小与所测金属晶粒大小均匀、晶界清晰、仪器状态良好、检测人员水平接近、直线截点法本身的测定精度较高等因素有关,试验过程中要注意这些因素的控制。     

GB/T 6394-2017在钛合金晶粒度评定中的应用

对各类钛合金的晶粒度评定做了定义。应用GB/T 6394-2017中的比较法和截点法对α,β类钛合金材料的晶粒度进行了评定。对α-β两相合金中出现的等轴组织、双态组织、网篮组织、魏氏组织、非等轴组织及特殊组织的晶粒度评定方法做了应用研究。结果表明:α,β类单相钛合金、各相含量明确的α-β两相钛合金及再结晶热处理后的超细晶组织,均可应用GB/T 6394-2017中比较法和截点法来进行晶粒度评定。     

GB/T 6394—2002《金属平均晶粒度测定法》存在的问题

从理论和实际应用两方面对GB/T 6394—2002《金属平均晶粒度测定法》中,通过加热处理形成奥氏体晶粒度的方法存在的问题进行分析,并提出了修订建议,即对金属经过加热方法所形成的晶粒度和不经过任何加热处理直接侵蚀得到的晶粒度应进行区分,并提出"标准晶粒度"的概念以区分"实际晶粒度"。     

金相检验(试验)技术标准目录汇编(一)

1 通用金相检验技术标准GB/T 4342—1991《金属显微维氏硬度试验方法》GB/T 5030—1985《金属小负荷维氏硬度试验方法》GB/T 7232—1987《金属热处理工艺术语》GB/T 11250.1—1989《复合金属覆层厚度的测定金相法》GB/T 13298—1991《金属显微组织检验方法》GB/T 15749—1995《定量金相手工测定方法》ZB N 71004—1987《标准显微维氏硬度块》YB/T 5148—1993《金属平均晶粒度测定方法》2 有关钢的金相检验技术标准GB/T 224—1987《钢的脱碳层深度测定方法》GB/T 225—1988《钢的淬透性末端淬火试验方法》GB/T 226—1991《钢的低倍组织及缺陷酸蚀检验法》     

用氧化法显示高碳钢奥氏体的晶粒度

显示奥氏体晶粒度,对金相人员来说是一难点。实验证明:钢中随着碳含量的增加,用晶界腐蚀法显示难度也随之增大。尤其当钢中碳含量超过共析钢成分时,显示奥氏体晶界更为困难。众所周知,金属的化学活性在其晶界和晶内是不同的,晶界上的金属具有较大的活性,易氧化,当试样加热时,试样表面上形成的氧化物(Fe+O_2→FeO(Fe_2O_3)其各处厚度不等,晶粒边界的氧化物比晶粒内部的氧化物厚,经适当的研磨、抛光后,仅晶界有氧化物。根据氧化物来显示晶粒,以确定奥氏体晶粒度氧化法正是利用这一原理。有文献介绍:氧化法有两种方法,一种将磨制好的试样在保护剂中加热,然后短时间强烈氧化;另一种方法,是直接把磨制好的试样暴露在氧化气氛中加热氧化,但具体操作及注意事项不详。本文采用的氧化法与以上介绍的两种方法略有不同,现介绍如下。     

光学显微镜检测金属晶粒平均截距的不确定度评定

根据JJF 1059-1999和GB/T 6394-2002,采用光学显微镜及金相图像分析软件对某钢的晶粒进行了平面观察和测量,放大200倍观察,按直线截点法检验,对检测金属晶粒平均截距的测量不确定度来源进行了分析,并对每个不确定度分量进行了评定,最终给出了扩展不确定度及测量结果的不确定度报告。结果表明:钢的金属晶粒平均截距测量结果的不确定度报告为,平均截距的测量值为(23.7±0.6)μm,k=2。     

异步轧制Pb-Ca-Sn-Al合金晶界节点分形分析

为了确定晶界节点分形维数是否存在,以低碳钢冷轧薄板标样为研究对象,在MATLAB软件平台上自行开发了晶界分形维数计算程序,采用标准分形图形-koch曲线检验了自开发分形程序的准确性,利用该程序计算了3种标准下(不同晶粒延伸度)不同晶粒度级别的金相图片晶界节点分形维数,并研究了不同工艺条件下Pb-Ca-Sn-Al合金晶界节点的分形维数.结果表明:自开发的分形计算程序准确;晶界节点的分形维数存在;不同工艺条件Pb-Ca-Sn-Al合金晶界节点的分形维数与工艺参数之间存在定量联系.在一定范围内,随着压下率、异速比、退火温度的增加,晶界节点的分形维数随之增加;随退火时间的增加,Pb-Ca-Sn-Al合金晶界节点分形维数先上升后下降;退火张力增加,晶界节点分形维数下降.     

T91钢焊缝及热影响区显微组织图象分析

T91钢具有良好的高温抗氧化性和抗腐蚀性,该钢含8％－9．5％Cr,合金含量复杂,焊接难度大,运用金相显微镜和扫描电镜（SEM）分析了不同爆接工艺条件下T91耐热钢焊缝及热影响区或区域显微组织特征,利用XQF－2000型显微图象分析仪对显微组织中各相的相对含量和奥氏体晶粒度进行了测量,分析了焊接线能量对T91钢焊接接头区组织性能的影响,结果表明,采用多道焊焊接工艺,严格控制焊接线能量在16kJ/cm左右,可以防止T91钢焊缝区奥氏体晶粒粗大,避免在热影响区出现声状铁素体组织,从而保证焊接接头区具有良好的组织性能。     

Synthesis of W-Y_2O_3 alloys by freeze-drying and subsequent low temperature sintering:Microstructure refinement and second phase particles regulation

In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(<20 nm)exist in W matrix.Moreover,many Y6 WO12(<10 nm)particles exist within submicron Y2 O3 particles.The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase boundaries.The combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 HV0.2.Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys.     

Study on electrical properties of Ni-doped SrTiO3 ceramics using impedance spectroscopy

The ceramics, SrTiO₃ (ST) and 0.4, 0.8 atom % Ni doped SrTiO₃, were prepared by solid state reaction route. The average grain size of undoped and doped samples was measured and found to be 1.2, 1.9 and 3.7 μm, respectively. The impedance measurements were conducted at 400–600°C to separate grain and grain boundary contributions. The grain and grain boundaries relaxation frequencies were shifted to higher frequency with temperature. Bulk resistance of doped and undoped ST ceramics was more or less the same. Single grain boundary resistance of doped sample was higher than that of undoped one, indicating that GB resistance increases with acceptor doping. Activation energies were calculated to confirm the same.     

Effect of Grain Size on the Weldability of Cast Alloy 718

Electron beam welding was conducted on cast alloy 718 with varying grain sizes obtained using Microcast (MX™) and conventional cast (CC) techniques. The average value per section of Total Crack Length (Av. TCL) was measured on each cross section and used to represent the material's weldability. It was found for the first time that the grain size had a reduced effect on the weldability of cast alloys, relative to that reported in the literature for wrought alloys; i.e., increased grain size in the range of 90-3000 microns resulted in improved weldability. This was determined to be related to the probability of welds intersecting grain boundaries and causing grain boundary microfissuring. The conclusion from the experimental analysis is corroborated by the use of a Weibull-type analysis to evaluate the probability of a weld microfissure occurring relative to the grain size. As grain size increases, the probability of the weld intersecting the grains is reduced, and thus, the likelihood of microfissuring is reduced. With regard to a single crystal, there are no grain boundaries intercepting the weld (probability = 0), and thus, microfissuring related to constitutional liquation of primary carbides, or segregation of species to grain boundaries would not occur.     

基于频谱能量的材料晶粒尺寸表征方法

研究了利用超声频谱能量对材料晶粒尺寸进行表征的方法。通过不同的热处理方式获得了不同晶粒尺寸的奥氏体不锈钢材料,再分别利用衰减系数法、声速法和频谱能量法对材料的晶粒尺寸进行表征。结果表明:频谱能量法得到的衰减系数与平均晶粒尺寸呈非线性关系,晶粒尺寸的预测误差在4%~15%以内,优于传统的分析方法,证明了新方法的有效性。     

Improvement of the Grain Refinement of Cu-Zn-Al Shape Memory Alloys with Manganese,Cobalt, and Zirconium Addition

The objectives of the present work were to determine the best grain refiners for copper-based shape memory alloys among three of the most important elements, to evaluate the kinetic grain growth, and to observe the changes produced in the transformation temperatures and enthalpies with the grain size for each alloy, in various fine-grained Cu-Zn-Al shape memory alloys. Image analysis and calorimetry techniques were used. The study shows that grain boundaries favor martensitic transformation and, at the same time, obstruct retransformation.     

Biodegradation mechanisms of selective laser-melted Mg–xAl–Zn alloy: grain size and intermetallic phase

Grain size and intermetallic phase were two key factors affecting the biodegradation behaviour of Mg alloys. In the paper, different grain size and intermetallic phase volume fraction were obtained by introducing Al into Mg–Zn alloy via selective laser melting. Results showed that the grain size refined while the intermetallic phase volume fraction increased with Al increasing. As Al was less than 3?wt.%, the grain refinement was the major factor affecting the degradation behaviour. The finer grain would create many grain boundaries, making the alloy passivate readily and resulted in a reduced degradation rate. However, with Al further increasing, the intermetallic phase became the main factor influencing the degradation behaviour though grain size was further refined. The large intermetallic phase volume fraction caused severe galvanic corrosion, accelerating the degradation. This work may provide guidance for balancing grain size and intermetallic phase on degradation behaviour of Mg alloys.     

Magnetically induced abnormal grain growth in pure nickel

The evolution of the microstructure of cold-rolled pure Ni during annealing at 300–800°C for 120?min with and without a high magnetic field of 10?T was investigated. When the direction of the field was either parallel or perpendicular to the sample rolling direction (RD), the average grain size of the cube grains decreased, and abnormally grown grains with random orientation were observed. The migration of different kinds of grain boundaries, including Cube–Cube (C–C) grain boundaries, Cube–Non-cube (C–N) grain boundaries, and Cube–Abnormal (C–A) grain boundaries, was also investigated. The driving force produced by the magnetic field accelerated the migration of C–A grain boundaries, which reasonably explained the formation of abnormal growth.     

冷却槽对自孕育法制备ZA92镁合金组织的细化作用

采用自孕育法制备新型的ZA92镁合金,研究了冷却槽对组织的细化作用,并对其机理进行了分析。结果表明:合金熔体内部的形核与冷却槽的激冷作用、熔体的流动速度及剪切力的大小有关,合适的冷却槽角度有利于晶粒的游离和增殖。熔体在流经冷却槽的过程中,其组织变化趋势为:粗大枝晶→细小枝晶→等轴晶→蔷薇状晶和近球状晶。冷却槽角度较大或较小均不利于组织的细化,当冷却槽角度在30~45°之间时,坯料组织的晶粒分布比较集中且细小,其平均晶粒尺寸在47.5~51.4μm之间。     

Grain Boundary Sliding at Serrated Grain Boundaries

A constitutive model is developed for grain boundary sliding (GBS) at serrated grain boundaries. Based on a previously developed GBS model, using the dynamics of grain boundary dislocation pile-up, the present model takes the average of the sliding rate over the characteristic dimensions of grain boundary serrations. Thus, a geometric factor is introduced to account for the effects of serration wave length and amplitude on the GBS rate, as compared to the GBS rate at planar boundaries. By considering the role of grain boundary shear stress in stress balancing, the proposed model removes the singularity at planar boundaries which exists in the diffusion-controlled GBS model at serrated grain boundaries. The modified model describes very well the transient creep of complex Ni-base superalloys with and without grain boundary serrations and should be suitable for other engineering alloys (with the exception of columnar grained and single crystal alloys).     

全层状TiAl基合金断裂中晶界的双重作用

通过SEM原位拉抻技术和双晶体压缩实验研究了全片层TiAI基合金晶界断裂行为。研究表明,在全层状组织的断裂行为中,晶界具有双重作用。一方面,微裂纹首先萌发于晶界区,其扩展方式取决于晶界两侧片层的取向。另一方面,不同类型的晶界对裂纹扩展的阻力不同,因而对全层状TiAI基合金韧性的作用不同,纵向晶界有助于断裂韧性的提高,而横向晶界对合金韧性不利。