新式布局的真空等轴晶精密铸造炉

本文论述了一种新式布局的真空等轴晶精密铸造炉,该设备是为了替代传统立式等轴晶精密铸造炉,用于生产薄壁、大尺寸铸件及低温浇铸件等.它采用了卧式布局、内置模壳加热器、同轴水冷电缆、线圈平移机构等一系列创新理念与技术.该设备还具有良好的扩展功能,通过更换功能部件可实现细晶铸件的生产.     

高强铸造铝合金的DAS与机械性能关系的研究

在一般的铸造条件下,铸件多为树枝晶组织,根据成分过冷的大小可形成一次、二次、三次分枝。一般认为二次枝品间距(DendriteArm Spacing,以下简称DAS)对铸件机械性能的影响较大。凝固理论的研究表明,合金成分一定时,DAS仅决定于铸件的凝固时间。Kattmis等根据枝晶粗化理论得到     

小波神经网络在超声检测信号中降噪的研究

摘 要: 为了最大限度的消除粗晶材料超声检测时,晶粒散射波对有用信号的严重干扰,提高接收信号的信噪比,将小波神经网络引入粗晶材料超声检测信号处理领域中。在训练小波神经网络时,采用了改进的梯度下降算法。该网络有一个动态的权值,它随误差变化而调整。结果表明,小波神经网络应用在粗晶材料超声检测信号的降噪时,能够达到较理想的降噪效果。     

阻力板断裂原因分析

应用扫描电镜、光学显微镜和光谱分析等手段．分析了RZG45熔模精密铸件产生脆性断裂的原因。结果表明，铸件的断裂系由呈链状沿晶分布的脆性相所致。提出了消除脆性相的措施。     

模具定量精确成形技术在挤铸生产中的应用 研究

目的解决小型铝合金挤压铸件在浇铸过程中,存在的浇铸质量误差大、铸件组织的一致性较差、热节区出现组织缩松的问题,同时提高材料利用率。方法将模具定量精确成形技术引入到实际生产。结论模具定量精确成形技术的应用,能够有效解决小型铝合金挤压铸件在浇铸过程中因浇铸质量误差大的问题,铸件的总体质量误差能够控制在±0.02 kg范围以内,有效解决了因铸件质量误差大造成的铸件壁厚误差大,解决了铸件组织的一致性较差、热节区出现组织缩松的问题,提高了材料的利用率。     

新型钛精铸氧化物陶瓷型壳工艺研究EI

叙述了一种适合于制造薄壁钛合金精密铸件的新型制壳工艺，研究试验了型壳面层用稳定的氧化物耐火材料和稀土粘结剂，分析讨论了新工艺所浇铸的钛精铸件的冶金质量与性能。     

300M超高强度钢的奥氏体相变再结晶温度和低倍粗晶的消除

利用高温金相、热处理等手段测定了飞机起落架用超高强度钢３００Ｍ的奥氏体相变结晶温度。试验结果表明，３００Ｍ钢的奥氏体相变再结晶发在一温度区间，此温度区间的高低受加热方式，原始组织的影响，根据试验结果，确定了消除３００Ｍ钢低倍粗晶的热处理工艺。     

小波神经网络在超声检测信号降噪中的应用

为了最大限度地消除粗晶材料超声检测时,晶粒散射波对有用信号的严重干扰,提高接收信号的信噪比,将小波神经网络引入粗晶材料超声检测信号处理领域中.在训练小波神经网络时,采用了改进的梯度下降算法.该网络有一个动态的权值,它随误差变化而调整.结果表明,小波神经网络应用在粗晶材料超声检测信号的降噪时,能够达到较理想的降噪效果.     

铜合金铸件着古铜色后的清洗方法

铜合金铸件着古铜色后的清洗方法南京电影机械厂（２１００４２）华树芳铜合金铸件成型简单，节省工序，加工方便，节约铜材，目前在灯具、汽车及装饰行业中被广泛应用。但从铜合金浇铸工艺来看，不管采用那种模具浇铸，不同程度上存在着砂眼、气孔、缩孔等缺陷。尤其是经...     

K417合金细晶铸造热参数的研究

本文研究了Ｋ４１７合金的细晶铸造热工艺参数，研究结果表明，当型壳温度控制在９００～１０００℃，浇注温度控制在Ｐ＋２９℃～Ｐ＋５０℃时，可获得健全的Ｋ４１７细晶铸件，与普通铸件相比，其低周疲劳寿命提高２～３倍。     

Behaviour of sand–clay mixtures for road pavement subgrade

Materials forming sand grains and colluvial soil deposits have a distinct structure, consisting of a composite matrix of coarse and fine soil grains. The influence of sand grains content on the behaviour of sand–clay mixtures was investigated by a series of intensive laboratory experiments. The California bearing ratio (CBR), unconfined compression strength (UCS) and compaction tests were carried out on various contents of sand and clay mixtures. The sand–clay mixtures were prepared with sand contents of 0, 10, 20, 30, 40, and 50% by weight. The laboratory tests on these mixtures have indicated that their behaviour will depend on the relative concentration of the sand and clay samples. The results of the tests showed a decrease in the UCS, and an increase the CBR values with an increase in the amount of sand. An increase in dry unit weight and a decrease in respective moisture content by an increase in the amount of sand were observed in the compaction tests.     

ODS ferritic steel engineered with bimodal grain size for high strength and ductility

An attractive way to enhance the ductility of ODS ferritic steels is to develop an alloy with a bimodal grain size distribution, in which the micron-sized coarse grains provide high ductility. The nanometer-sized fine grains enhance the tensile strength. The microstructures were obtained by blending the gas-atomized powders and mechanical alloyed powders, followed by hot forging and annealing. The homogeneously distributed nanometer-sized oxide nanoparticles can also be detected. Mechanical properties tests revealed a great improvement in ductility in comparison with other ODS ferritic steels, and high strength over the whole range of test temperatures, owing to the fine grains and oxide nanoparticles. The combination of high ductility and high strength makes this ODS ferritic steel much promising in high-temperature application.     

Methods and mechanisms for uniformly refining deformed mixed and coarse grains inside a solution-treated Ni-based superalloy by two-stage heat treatment

The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate some δ phases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT tem-perature is 980℃.The phenomenon attributes to the uneven distribution of δ phase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number of δ phases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with few δ phases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prereq-uisite to precipitate even-distributed δ phase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation around δ phase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).     

Thermal stability and mechanical properties of nanostructured Ti–24Nb–4Zr–7.9Sn alloy

Thermal stability of the nanostructured grains of cold-rolled Ti–24Nb–4Zr–7.9Sn alloy and corresponding variations in mechanical properties were investigated. The activation energy for grain growth was found distinct below and above the ( + β)/β transus of 950 K, with values of 47 and 206 kJ/mol, respectively. Due to the pinning effect of the precipitates at β grain boundaries, grains sizes can be maintained at less than 100 nm during prolonged annealing at temperatures up to 773 K, and are less than 1 μm for annealing temperature up to 923 K and time up to 2 h. Annealing above the β transus resulted in coarse grains with sizes of tens of micrometers in less than 2 h. Tensile and hardness tests showed rapid strengthening with the increase of annealing time below 773 K, which was attributed to both the rapid formation of nano-sized precipitates and the slow growth rate of β grains. By adjusting the grain size of the cold-rolled material the high strength/low Young's modulus match desirable for implant applications can be improved over the hot-rolled bars with coarse grains.     

纳米改性金属陶瓷的组织和力学性能

讨论了纳米TiN改性TiC基金属陶瓷(纳米改性金属陶瓷)的组织与力学性能。结果表明,金属陶瓷组织仍为两相结构(陶瓷相+金属相),其中粗大的陶瓷相为芯/壳结构,即Ti(C,N)芯外包覆有一层硬质相(Ti,Mo,W)(C,N)(即"SS"相)。TEM观察显示,纳米TiN主要在两相或三相晶界上分布。随纳米TiN的增加,纳米改性金属陶瓷的组织明显细化;组织的细化与纳米TiN在TiC/TiC晶界的分布阻止了TiC晶粒的长大有关。抗弯测试表明,抗弯强度在添加8 wt%纳米TiN时达到最大值;抗弯断口显示沿晶断裂为主要的断裂模式。     

Development of microstructure in isothermally forged Nimonic alloy AP1

Abstract

The development of microstructure in the nickel alloy Nimonic AP1 owing to isothermal forging and subsequent heat treatment has been investigated. The microstructure initially consisted of coarse grains, which corresponded to the prior powder particles; these were surrounded by a coarse dispersion of γ′. On deformation, the volume fraction of material with a coarse γ′ dispersion increased, and this was associated with localised grain refinement following heat treatment. High volume fractions of this structural type gave some increase in tensile strength but reduced stress rupture life and increased fatigue crack growth rates. High temperature compression tests were used to develop a constitutive equation for the material which was then applied, via a finite element model, to simulate the isothermal forging process. The relationships between deformation and structural development, the modelling, and the mechanical properties are discussed. The approach is potentially useful for the design of forging operations for turbine disc production.     

Study on the microstructure and mechanical properties of explosive welded 2205/X65 bimetallic sheet

In this study, microstructural inhomogeneity and mechanical properties of explosive welded 2205 stainless steel/X65 pipe steel bimetallic sheets were investigated. The explosion-bonded 2205/X65 bimetallic sheets had good shear strength. The tensile shear fracture primarily occurred in the interior of X65 material and primarily exhibited dimple morphology. Fine crystal grains in the 0.5–2 μm range were found all over the narrow localized melted zone near the 2205/X65 interface, whereas a coarse columnar crystal structure growing along the perpendicular direction to the interface formed in the wider localized melted zone. Quasi-cleavage fracture morphology was observed in the coarse columnar crystal region after the stratified tensile test. The junction of the three regions near the interface with large differences in morphology was the weak point in the bimetallic sheet, where Y-shaped cracking easily occurred under a loading force. Stratified tensile test and micro-hardness tests for the explosively welded bimetallic sheet showed that severe hardening occurred in the 2205 cladding, and the most severe metal hardening occurred near the interface. Tests for 45° face bending and root bending tests were conducted under extreme conditions. The results showed that voids were prone to appeared in the peninsula and island morphologies near the interface.     

点焊熔核“柱状+等轴”组织形成机理分析

LY12CZ(A2024-JIS)铝合金板材点焊熔核的凝固组织是由柱状组织和等轴组织共同组成。本文利用光镜和扫描电镜不仅反映了熔核的“柱状+等轴”组织形貌,而且直观、精细地揭示出其组成单元——粗大柱状晶和粗大等轴晶(本文命名)的内部结构及形态特征,并从结晶机理上作了分析,进一步提出了点焊熔核“柱状+等轴”组织形成过程模型。     

Optimizing mechanical property and cytocompatibility of the biodegradable Mg-Zn-Y-Nd alloy by hot extrusion and heat treatment

The Mg-Zn-Y-Nd alloy is a new type of degradable material for biomedical application. In the present study, Mg-6Zn-1.2Y-0.8Nd alloy was fabricated, and then extrusion and heat treatment were conducted to optimize its mechanical properties and cytocompatibility. The microstructure observation, mechanical property, degradation behavior and cytocompatibility tests were conducted on the Mg-Zn-Y-Nd alloy with three different states: as-cast (alloy C), as-extruded (alloy E) and extruded + heat treated (alloy EH). The results show that alloy C consists of coarse grains and continuous secondary phases. The extrusion process has caused incomplete recrystallization, and results in a mixed grain structure of elongated grains and small equiaxed grains (alloy E). The heat treatment process has promoted the recrystallization and homogenized the grain structure (alloy EH). Both the strength and ductility of the alloy has been improved by extrusion, but the following heat treatment has decreased the strength and increased the ductility. The degradation behavior of the alloy C and E alloys does not show much difference, but improves slightly in alloy EH, because the heat treatment has homogenized the microstructure and released the residual stress in the alloy. The directly and indirectly cell viability tests indicate that alloy EH exhibits the best cytocompatibility, which should be ascribed to its relative uniform degradation and low ion releasing rate. In summary, the combination of hot extrusion and heat treatment could optimize the mechanical property and cytocompatibility of the Mg-Zn-Y-Nd alloy together, which is beneficial for the future application of the alloy.     

On the feasibility of ultrasonic NDE to estimate the bond quality of diffusion-welded joints

A set of 14 diffusion-bonded test specimens with different bond qualities has been investigated by ultrasound using compressional and shear waves at normal incidence with frequencies from 2–15 MHz. The ultrasonic test results, double way transmission-to-reflection ratio and signal-to-noise ratio, have been correlated to the results of tensile tests and notched-bar toughness tests. Defects observed in metallographic and SEM images from the diffusion bonds are narrow long strips (unbonded valleys originating from the surface roughness and from coarse grains in the grinding wheel), flat areas in the bond line without enough recrystallization (areas in which the diffusion process was inhibited), and contamination with alumina powder in the bond plane. In order to gain a deeper understanding of the ultrasonic interaction with these defects and to predict optimal inspection parameters, the ultrasonic scattered amplitude has been calculated using a quasi-static model and has been compared to the experimental results. Except for the bond contaminated by alumina powder, the ultrasonic experimental data, the model calculations, and the mechanical test results are well correlated.