粉末烧结体热复压变形力的工程计算

阐述用机械压力机进行粉末热锻时 Fe- 0 .2 2 C粉末烧结体热复压变形力的工程计算 .在相同温度下进行粉末烧结体热复压 ,锻造力的增加往往使锻造密度也增加 .介绍了粉末烧结体热复压试验用的设备、材料及方法 .通过热复压变形测定了一定锻造温度下的真实屈服应力 σs.根据Kuhn关于多孔预制坯的屈服准则和热复压时的应力应变关系提出复压力的理论公式 ,可导得简化的热复压变形力的工程计算公式 .本公式对粉末锻造实际生产有一定的实用意义 .

铜铁烧结热复压工艺

本文以交流接触器零件动触桥为例，介绍了铜铁烧结热复压工艺参数、模具设计及金相检验等。这一项目的研制成功填补了国内空白，并具有显著的经济效益。

基于极限学习机的复材热压工段动态调度研究

单一启发式规则在复材热压成型工段动态调度中受到调度环境变化的影响,无法始终取得较高的热压罐利用率。为此,提出一种基于极限学习机的热压成型工段动态调度方法,从历史调度相关数据中提取训练样本数据,利用极限学习机学得有用的调度知识模型,拟在每一个调度决策时刻,根据实时的调度环境定出最佳工件排入罐中。以某复材车间热压成型工段为例进行研究。仿真实验表明:该方法较单一启发式规则能表现出更加稳定且良好的调度结果。

神舟七号飞船气闸舱热试验方法

简要介绍了神舟七号出舱活动飞船气闸舱单舱热试验(包括热平衡试验和泄复压热试验)情况,分别给出了试验技术状态、试验工况、试验过程及典型的试验结果等,重点论述了舱段级热试验所采取的通风对流换热模拟、流体回路换热模拟、固体传热边界模拟的关键技术。将试验结果与飞行遥测数据进行了比对分析,两者一致性很好,表明所采取的热边界模拟方法合理正确,舱段级热试验获得了成功,达到了缩短研制周期、节约研制经费的预期目的。

Mechanical Properties and Thermal Shock Resistance of SrAl_(2)Si_(2)O_(8) Reinforced BN Ceramic Composites

Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their densification during sintering still poses challenges for researchers,and their mechanical properties are rather unsatisfactory.In this study,SrAl_(2)Si_(2)O_(8)(SAS),with low melting point and high strength,was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness.Then,BN-SAS ceramic composites were fabricated via hot press sintering using h-BN,SrCO_(3),Al_(2)O_(3),and SiO_(2) as raw materials,and effects of sintering pressure on their microstructure,mechanical property,and thermal property were investigated.The thermal shock resistance of BN-SAS ceramic composites was evaluated.Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl_(2)Si_(2)O_(8).With the increase of sintering pressure,the composites’densities increase,and the mechanical properties shew a rising trend followed by a slight decline.At a sintering pressure of 20 MPa,their bending strength and fracture toughness are(138±4)MPa and(1.84±0.05)MPa·m^(1/2),respectively.Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion,with an average of 2.96×10^(-6) K^(-1) in the temperature range from 200 to 1200℃.The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^(-1)·K^(-1) within the temperature range from room temperature to 1000℃.Notably,BN-SAS composites exhibit remarkable thermal shock resistance,with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400℃.The maximum residual bending strength is recorded at a temperature difference of 800℃,with a residual strength retention rate of 101%.As the thermal shock temperature difference increase,the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.

粉末冶金论著中术语和用词辨析二十一题(4)

18表达不清读科技文章就怕文字表达不清。对表达不清的句子不易弄明白甚至产生误解,举例如下。1关系混乱和自相矛盾例1马氏体是碳溶解于α铁中的过饱和固溶体,集中有多种强化机制的作用,强度、硬度、磁饱和强度很高,是钢最有效、最经济的强化手段。

Experimental and simulation research on thermal stamping of carbon fiber composite sheet

To improve the manufacture efficiency and promote the application of composites in the automobile industry, a new composite forming method, thermal stamping, was discussed to form composite parts directly. Experiments on two typical stamping processes, thermal bending and thermal deep drawing, were conducted to investigate the forming behavior of composite sheets and analyze the influence of forming temperature on the formed composite part. Experimental results show that the locking angle for woven composite is about 30°. The bending load is smaller than 5 N in the stamping process and decreases with the increase of temperature. The optimal temperature to form the carbon fiber composite is 170 ℃. The die temperature distribution and the deformation of composite sheet were simulated by FEA software ABAQUS. To investigate the fiber movement of carbon woven fabric during stamping, the two-node three-dimension linear Truss unit T2D3 was chosen as the fiber element. The simulation results have a good agreement to the experimental results.

Influence of FeCrAl fiber on microstructure and mechanical properties of FeCrAl(f)/HA composites

FeCrAl fiber-reinforced hydroxyapatite（HA） biocomposites（FeCrAl（f）/HA） were fabricated by the hot pressing technique.The metallographic microscopy,X-ray diffractometry,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS） were used to observe and analyze the microstructure and composition of FeCrAl（f）/HA composites,respectively.The mechanical properties of FeCrAl（f）/HA composites were measured by the three-point-bending test.The results show that the composite can be reinforced by FeCrAl fiber and enhanced gradually,and then declined with the increase of the content of FeCrAl fiber（0-11%,volume fraction） in the whole range of experiments.Both the HA matrix and FeCrAl fiber integrate very tightly and bit into each other very deeply and counter-diffusion takes place to some extent at two-phase interface.The optimum parameters of FeCrAl（f）/HA composite are diameter of 22 μm,length of 1-2 mm and of volume faction of about 7% for FeCrAl fibers.

Effects of heat treatment on phase contents and mechanical properties of infiltrated B_4C/2024Al composites

The B4C/2024Al composites were successfully produced by pressureless infiltration method, and the effects of heat treatment on phase content and mechanical properties were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and mechanical properties testing. The results show that phases of BnC/2024Al composites include B4C, Al, Al3BC, AlB2 and Al2Cu. The phase species remain unchanged; however, the phase content of the composites changes significantly after heat treatment at the temperature of 660, 700, 800 or 900 ℃ for 12, 24 or 36 h. It is found that the heat treatment results in not only considerable enhancement in hardness, but also reduction in bending strength of the composites. Heat treatment at 800 ℃ for 36 h does best to hardness of the composites, while at 700 ℃ for 36 h it is the most beneficial to their comprehensive mechanical properties.

Flow stress behavior and processing map of extruded 7075Al/SiC particle reinforced composite prepared by spray deposition during hot compression

Hot compression tests of the extruded 7075Al/15%SiC (volume fraction) particle reinforced composite prepared by spray deposition were performed on Gleeble?1500 system in the temperature range of 300?450 °C and strain rate range of 0.001?1 s?1. The results indicate that the true stress?true strain curve almost exhibits rapid flow softening phenomenon without an obvious work hardening, and the stress decreases with increasing temperature and decreasing strain rate. Moreover, the stress levels are higher at temperature below 400 °C but lower at 450 °C compared with the spray deposited 7075Al alloy. Superplastic deformation characteristics are found at temperature of 450 °C and strain rate range of 0.001?0.1 s?1 with corresponding strain rate sensitivity of 0.72. The optimum parameters of hot working are determined to be temperature of 430?450 °C and strain rate of 0.001?0.05 s?1 based on processing map and optical microstructural observation.

Microstructures and mechanical properties of 2024Al/Gr/SiC hybrid composites fabricated by vacuum hot pressing

The 2024Al/Gr/SiC hybrid composite plates with 5%-10% SiC particles （volume fraction） and 3%-6% flaky graphite （Gr） （volume fraction） were fabricated by vacuum hot pressing and hot extrusion processing. The effects of SiC and Gr on the microstructures and mechanical properties of the composites aged at 160, 175 and 190℃ were studied by optical microscopy, scanning electron microscopy （SEM）, and hardness and tensile tests. The results indicate that the SiC particles have a more obvious effect on accelerating the aging response as compared with the Gr. Both the tensile strength and elongation are reduced by the Gr and SiC particles added into the matrix, while the Gr has a more negative influence on the elongation than the SiC particles. The tensile strength （ab）, yield stress （as） and elongation （δ） of the 2024Al/3Gr/10SiC composite aged at 165℃ for 8 h are 387 MPa, 280.3 MPa and 5.7%, respectively. The hybrid composites are characterized by ductile fracture, which is associated with the ductile fracture of the matrix and the tearing of the interface between the matrix and the particles.

Fabrication and mechanical properties of Ti_(2)AlC/TiAl composites with co-continuous network structure

Ti_(2)AlC/TiAl composites with different volume fractions were prepared by hot pressing technology,and their reinforced structural characteristics and mechanical properties were evaluated.The results showed that when the reinforced phase volume fraction of Ti_(2)AlC was 20%,three-dimensional interpenetrating network structures were formed in the composites.Above 20%,Ti_(2)AlC phase in the composites accumulated and grew to form thick skeletal networks.The microplastic deformation behavior of Ti_(2)AlC phase,such as kink band and delamination,improved the fracture toughness of the composites.Comparative analysis indicated that the uniform and small interconnecting network structures could further reinforce the composites.The bending strengths of composites prepared with 20 vol.%Ti_(2)AlC reached(900.9±45.0)MPa,which was 25.5% higher than that of TiAl matrix.In general,the co-continuous Ti_(2)AlC/TiAl composite with excellent mechanical properties can be prepared by powder metallurgy method.

Effect of hot extrusion on microstructure and tribological behavior of Al_(2)O_(3p) reinforced 7075 aluminum-matrix composites

The effects of hot extrusion and addition of Al_(2)O_(3p) on both microstructure and tribological behavior of 7075 composites were investigated via optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),and transmission electron microscopy(TEM).The experimental consequences reveal that the optimal addition of Al_(2)O_(3p) was 2 wt%.After hot extrusion,the Mg(Zn,Cu,Al)2 phases partially dissolve into the matrix and generate many uniformly distributed aging precipitation particles,the Al_(7)Cu_(2)Fe phases are squeezed and broken,and the Al_(2)O_(3p) become uniform distribution.The microhardness of as-extruded 2 wt%Al_(2)O_(3p)/7075 composites reaches HV 170.34,increased by 41.5%than as-cast composites.The wear rate of as-extruded 2 wt%Al_(2)O_(3p)/7075 composites is further lower than that of as-cast composites under the same condition.SEM-EDS analyses reveal that the reinforced wear resistance of composites can put down to the protective effect of the Al_(2)O_(3p) reinforced transition layer.After hot extrusion,the transition layer becomes stable,which determines the reinforced wear resistance of the as-extruded composites.

Compressive response and microstructural evolution of in-situ TiB_(2)particle-reinforced 7075 aluminum matrix composite

The hot forming behavior,failure mechanism,and microstructure evolution of in-situ TiB_(2)particle-reinforced 7075 aluminum matrix composite were investigated by isothermal compression test under different deformation conditions of deformation temperatures of 300−450℃ and strain rates of 0.001^(−1)s^(−1).The results demonstrate that the failure behavior of the composite exhibits both particle fracture and interface debonding at low temperature and high strain rate,and dimple rupture of the matrix at high temperature and low strain rate.Full dynamic recrystallization,which improves the composite formability,occurs under conditions of high temperature(450℃)and low strain rate(0.001 s^(−1));the grain size of the matrix after hot compression was significantly smaller than that of traditional 7075Al and ex-situ particle reinforced 7075Al matrix composite.Based on the flow stress curves,a constitutive model describing the relationship of the flow stress,true strain,strain rate and temperature was proposed.Furthermore,the processing maps based on both the dynamic material modeling(DMM)and modified DMM(MDMM)were established to analyze flow instability domain of the composite and optimize hot forming processing parameters.The optimum processing domain was determined at temperatures of 425−450℃ and strain rates of 0.001−0.01 s^(−1),in which the fine grain microstructure can be gained and particle crack and interface debonding can be avoided.

Processing map and microstructure evaluation of AA6061/Al_2O_3 nanocomposite at different temperatures

Hot compression behavior of Al6061/Al2O3nanocomposite was investigated in the temperature range of350-500°C andthe strain rate range of0.0005-0.5s-1,in order to determine the optimum conditions for the hot workability of nanocomposite.Theactivation energy of285kJ/mol for the hot compression test is obtained by using hyperbolic sine function.By means of dynamicmaterial model(DMM)and the corresponding processing map,safe zone for the hot workability of AA6061/Al2O3is recognized attemperature of450°C and strain rate of0.0005s-1and at temperature of500°C and the strain rate range of0.0005-0.5s-1,with themaximum power dissipation efficiency of38%.Elongated and kinked grains are observed at400°C and strain rate of0.5s-1due tothe severe deformation.

Constitutive model for a new kind of metastable β titanium alloy during hot deformation

The constitutive model was developed to describe the relationship among flow stress,strain,strain rate,and deformation temperature completely,based on the characteristics of flow stress curves for a new kind of metastable β Ti2448 titanium alloy from isothermal hot compression tests,in a wide range of temperatures（1023-1123 K） and strain rates（63-0.001 s-1）.During this process,the adopted hyperbolic sine function based on the unified viscoplasticity theory was used to model the flow behavior of alloy undergoing flow softening caused by dynamic recovery（DRV） at high strain rates（≥1 s-1）.The standard Avrami equation was adopted to represent the softening mechanism attributed to dynamic recrystallization（DRX） at low strain rates（1 s-1）.Additionally,the material constants were determined by optimization strategy,which is a new method to solve the nonlinear constitutive equation.The stress—strain curves predicted by the developed constitutive model agree well with the experimental results,which con-rms that the developed constitutive model can give an accurate estimate of the-ow stress of Ti2448 titanium alloy and provide an effective method to model the flow behavior of metastable β titanium alloys during hot deformation.

Processing, characterization, room temperature mechanical properties and fracture behavior of hot extruded multi-scale B_4C reinforced 5083 aluminum alloy based composites

Microstructural characteristics and mechanical behavior of hot extruded Al5083/B4C nanocomposites were studied.Al5083and Al5083/B4C powders were milled for50h under argon atmosphere in attrition mill with rotational speed of400r/min.For increasing the elongation,milled powders were mixed with30%and50%unmilled aluminum powder(mass fraction)with meanparticle size of>100μm and<100μm and then consolidated by hot pressing and hot extrusion with9:1extrusion ratio.Hot extrudedsamples were studied by optical microscopy,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM),tensile and hardness tests.The results showed that mechanical milling process andpresence of B4C particles increase the yield strength of Al5083alloy from130to566MPa but strongly decrease elongation(from11.3%to0.49%).Adding<100μm unmilled particles enhanced the ductility and reduced tensile strength and hardness,but usingthe>100μm unmilled particles reduced the tensile strength and ductility at the same time.By increasing the content of unmilledparticles failure mechanism changed from brittle to ductile.

Optimizing consolidation behavior of Al 7068-TiC nanocomposites using Taguchi statistical analysis

The fabrication of high strength Al 7068？5%TiC （mass fraction） nanocomposite was studied by mechanical alloying and hot pressing routes. Considering densification importance and grain growth effects, hot pressing process conditions for producing bulk nanocomposite were optimized using statistical Taguchi method based on compressive strength achievement. The Taguchi results indicate that 30 min hot pressing under pressure of 500 MPa at 385 °C provides high compressive strength and hardness of 938 MPa and HV 265, respectively. More interestingly, analysis of variance proves that the applied pressure is the most influential factor for hot pressing of the nanocomposite. The contribution percentages of factors in hot pressing terms are as follows： applied pressure （61.3%）, exposed temperature （29.53%） and dwelling hot pressing time （4.49%）.

Microstructure and properties of alumina-silicon carbide nanocomposites fabricated by pressureless sintering and post hot-isostatic pressing

A1203/5%SIC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed （HIP）, which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of A1203 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, A12OJSiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed A1203/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the A1203/5%SIC nanocomposites by pressureless sintering and post HIP process.

The hot compressive deformation behavior of the metal matrix composites with the large whisker orientation

Finite element analysis was used to investigate the effects of whisker misalignment on the hot compressive deformation behavior of whisker-reinforced composites. The simulation provided the evolution of the stress field of the composites and the whisker rotation process. It is found that with increasing the angle of whisker misalignment the whisker rotation angle decreases. Meanwhile, the mechanical behaviors of the composites such as work hardening or strain softening are affected by the whisker orientation and rotation during the hot compressive deformation. The predicted results are in agreement with the experimental results.