Microstructure and properties of In situ Al/TiB2 composite fabricated by in-melt reaction method

A novel in situ reaction process-in-melt reaction method was developed. TiB₂ particles form in situ through the reaction of TiO₂, H₃BO₃, and Na₃AlF₆ in an aluminum alloy melt. The results showed that the in situ TiB₂ particles formed were spherical in shape and had an average diameter of about 0.93 μm. Moreover, the distribution of TiB₂ particles in the matrix was uniform. The interface between the TiB₂ particles and the matrix showed good cohesion. The tensile strength and the yield strength of the composite increase with increasing TiB₂ content. When TiB₂ particle content in the matrix was 10 vol pct, the tensile strength, yield strength, and elongation of Al-4.5Cu/TiB₂ composite were 417 MPa, 317 MPa, and 3.3 pct, respectively.     

粉末热挤压法制备Mg2B2O5w/6061Al复合材料的组织和力学性能研究

采用粉末冶金法制备了含量分别为5%、10%、15%、20%(体积分数,下同)的硼酸镁(Mg2B2O5)晶须增强6061铝基复合材料,利用SEM和EPMA研究了复合材料的微观组织,并测定了其力学性能。结果表明:在复合材料制备过程中Mg2B2O5晶须发生了破碎和折断,Mg2B2O5多以晶须团聚体的形式存在,出现尺寸为10~25μm的颗粒状增强体;Mg2B2O5晶须沿挤压方向定向排列,并且定向排列性随晶须含量的增加而减弱;复合材料的抗拉强度随着晶须含量的增加先升高后降低,并在晶须含量为15%时达到最大值191MPa,较基体合金增加16.5%;复合材料的伸长率随晶须含量的增加逐渐下降,当晶须含量为20%时降至最低值6.3%。     

Microstructural characterisation and mechanical properties of spark plasma-sintered TiB2-reinforced titanium matrix composite

Titanium and titanium matrix composites, reinforced with TiB₂ particles, have been synthesised by the spark plasma sintering method at 1050°C under 50?MPa pressure, using mixtures of 2.4?wt.-% TiB₂ and 97.6?wt.-% Ti powders. The changes in microstructural features and mechanical properties were investigated. XRD results and SEM observations confirm the formation of TiB whiskers as a result of the reaction between Ti and TiB₂. However, some unreacted TiB₂ particles have remained in the composite owing to the incomplete chemical reaction between matrix and additives. The measured mechanical properties demonstrate that the increase in hardness and tensile strength with TiB₂ addition is mainly attributed to the generation of TiB whiskers, increase in relative density and decrease in grain size, while the reduction in bending strength is possibly due to the plastic restraint imposed on the matrix by the TiB whiskers and unreacted TiB₂ particles.     

The wettability of carbon/TiB2 composite materials by aluminum in cryolite melts

Both pure TiB₂ and carbon/TiB₂ composites are potential cathode materials for aluminum reduction cells. An important requirement for this application is that the material be wetted by aluminum in cryolite melts. A sessile drop technique combined with X-ray radiography was used to measure the contact angle formed between aluminum and pure hot-pressed TiB₂, carbon/TiB₂ composite, graphite, and a carbonaceous cement in cryolite melts. Pure hot-pressed TiB₂ was found to be completely wetted by aluminum in cryolite melts. Graphite and the carbonaceous cement were nonwetted by aluminum in cryolite melts, the contact angles being in the range of 144 to 158 deg. The contact angle formed by aluminum on the carbon/TiB₂ composite in cryolite melts exhibited time dependency. It was proposed the time dependency was due to (1) removal of contamination from the composite surface and (2) removal of aluminum from the drop. The wettability of the composite material increased as the TiB₂ content increased.     

MoS_2对铝基材料摩擦磨损性能的影响

以Al,Fe,Zn等金属粉末和Si粉为原料,采用热压法制备MoS_2含量(质量分数)分别为0和3%的铝基复合材料,在滑动速度为0.377~1.131 m/s以及载荷为4~10 N的条件下进行摩擦试验,研究MoS_2对铝基复合材料摩擦磨损性能的影响。结果表明:在0.377 m/s的滑动速度下,3%MoS_2/铝基复合材料在10 N载荷下具有较低的平均摩擦因数0.4,比不含MoS_2材料的摩擦因数降低近一半;在0.755 m/s的滑动速度下,2种材料的摩擦因数和磨损率接近;在1.131 m/s的滑动速度下,载荷7~10 N时2种材料都严重磨损,3%MoS_2/铝基材料具有相对较低的磨损率,磨损机理为熔化磨损,未添加MoS_2材料的磨损机理为严重塑性变形磨损。添加3%MoS_2可显著改善铝基材料的摩擦磨损性能。     

The mechanism of formation of TiB2 particulates prepared by In Situ reaction in molten aluminum

By making use of a novel technique in which TiB₂ particulates are fabricated by an in situ reaction in molten aluminum, we have successfully produced TiB₂/Al composites. In order to reveal the characteristic of the technique, the mechanism of formation of TiB₂ particulates obtained by this method is studied in this article. Both theoretical and experimental results have shown that the TiB₂ particulates are formed by a diffusion mechanism when the molar fraction of aluminum in the preform is higher than 43.5 pct. In this case, the TiB₂ particulates are generally spherical, and their mean size is less than 2.0 μm. On the contrary, the TiB₂ particulates are formed by a solution-precipitation mechanism when the fraction is lower than 43.5 pct. In this case, the TiB₂ particulates are multifaceted, and the size of most particulates lies between 3.0 and 6.0 μgm.     

工业化制备7050铝合金厚板显微组织与力学性能

采用OM、TEM观察、室温拉伸试验,研究工业化制备大截面7050铝合金厚板微观显微组织和力学性能.结果表明:板材表层、1/4厚度层和芯部处均存在部分粗大晶粒组织以及晶粒尺寸分布不均匀现象,其中芯部粗大晶粒的尺寸、数量以及晶粒尺寸不均匀程度均高于1/4厚度层和表层;合金时效后晶内的析出相主要为η’相、η相以及少量GPⅡ区,表层晶粒内的析出相密度大于1/4层和芯部,且1/4层和芯部粗棒状的η相含量较高;合金的强度、硬度以及延伸率在厚度方向上呈梯度分布,表层硬度、抗拉强度（σ_b）、屈服强度（σ_0.2）和延伸率（δ）均最高,从表层到芯部,硬度、σ_b、σ_0.2以及δ均逐渐减小.      

Thermomechanical behavior of TiNi shape memory alloy fiber reinforced 6061 aluminum matrix composite

The processing and thermomechanical behaviors of TiNi shape memory alloy (SMA) fiber-reinforced 6061 Al matrix smart composites are investigated experimentally and analytically. Optimum processing conditions of hot pressing temperature and pressure are identified. Composite yield stresses are observed to increase with an increase in the volume fraction of TiNi fiber and prestrain given to the composites. An analytical model for thermomechanical behavior of the composites is developed by utilizing an exponential type of SMA constitutive model. The model predicts an increase in the composite yield stress with an increase in prestrain. It is found that the key parameters affecting the composite yield stress are the fiber volume fraction, prestrain, and matrix heat treatment. The predictions are in a reasonably good agreement with the experimental results.     

Thermomechanical behavior of TiNi shape memory alloy fiber reinforced 6061 aluminum matrix composite

The processing and thermomechanical behaviors of TiNi shape memory alloy (SMA) fiber-reinforced 6061 Al matrix smart composites are investigated experimentally and analytically. Optimum processing conditions of hot pressing temperature and pressure are identified. Composite yield stresses are observed to increase with an increase in the volume fraction of TiNi fiber and prestrain given to the composites. An analytical model for thermomechanical behavior of the composites is developed by utilizing an exponential type of SMA constitutive model. The model predicts an increase in the composite yield stress with an increase in prestrain. It is found that the key parameters affecting the composite yield stress are the fiber volume fraction, prestrain, and matrix heat treatment. The predictions are in a reasonably good agreement with the experimental results.     

硫酸铝铵原位分解制备Al2O3颗粒增强铝基复合材料

向铸铝ADC12熔体中添加脱水后的硫酸铝铵,反应分解的Al2O3原位生成颗粒增强铝基复合材料,该方法既可节约成本,同时由NH4Al（SO4）2分解的SO3对熔体具有精炼作用．SEM观察表明,Al2O3颗粒在铝基体中细小弥散分布,形成球形、不团聚的增强体颗粒．与基材相比,该复合材料的耐磨性明显提高;拉伸试验显示,复合材料的抗拉强度和延伸率有所降低．     

The processing and mechanical behavior of an aluminum matrix composite reinforced with short fibers

An aluminum alloy composite reinforced with chopped Al₂O₃ fibers randomly oriented in a plane has been produced by a modified squeeze casting process and its mechanical behavior compared with the corresponding behavior of the matrix. The specific characteristics of the compositing process have been examined vis-à-vis the characteristics of liquid metal infiltration into the capillaries of the fiber bundle. The flow stresses in the as-cast composite have been correlated with predictions based on continuum plasticity. Fracture of the fibers has also been characterized and interpreted using a weakest link statistical model, in conjunction with trends in the stress in the fibers. Changes in the composite flow stress caused by such fractures have been addressed. Finally, residual stress effects have been analyzed.     

Mechanical behavior of damage tolerant TiB whisker-reinforced in situ titanium matrix composites

The results of a systematic study of the effects of alloying and microstructure on the mechanical behavior of in situ titanium matrix composites are reported in this paper. In situ composites are produced by alloying with B which promotes the formation of TiB whiskers during rapid solidification processing. The composite powders are subsequently compacted and extruded to align the whiskers prior to systematic heat treatment in the β and/or α + β phase fields. The processing conditions for the development of in situ composites with attractive combinations of strength, ductility, damage tolerance and creep resistance are thus established. The improvements in the composite properties are rationalized using simple micromechanics principles. The paper highlights the potential for the microstructural design of composites using micromechanics and conventional physical metallurgy principles.     

Tribological properties of FeCoCrNiAlBx high-entropy alloys coating prepared by laser cladding

FeCoCrNiAlBx(x=0, 0.25, 0.50, 0.75) coatings were prepared by laser cladding to study the effects of boron on the structure and properties of high-entropy alloys coatings.The microstructure, microhardness, and wear resistance properties of the samples were investigated by scanning electron microscopy, X-ray diffraction, metallographic micro-hardness test, and friction-wear test, respec-tively, and the mechanism of the wear behavior was also analyzed.The results showed that the high-entropy alloys consisted of BCC phase and eutectic structure, which contained FCC phase and M2 B. With boron addition, the content of BCC phase increased while that of eutectic structure decreased. The wear resistance of the high-entropy coatings was considerably improved with increasing addition of boron, and accordingly, the FeCoCrNiAlB0.75 coating showed the best wear resistance.     

搅拌摩擦加工参数对5083铝合金组织性能的影响

采用搅拌摩擦加工方法对不同焊接参数下的退火态5083铝合金的组织和性能进行研究.通过显微硬度实验研究了硬度在前进侧和后退侧以及加工区上下部分的分布规律;通过金相观察研究了加工区表面带状纹理和腐蚀后观察到的弧纹之间的关系.对母材和加工区用扫描电镜观察了析出相的形貌、尺寸及分布规律.结果表明:高硬度区宽度随着轴肩直径的增大而增大,随着转速和焊速之比(ω/ν)的增加而增大,硬度在前进侧(AS)和后退侧(RS)的分布是不均匀的;从母材到加工区硬度逐渐上升,RS侧的上升速度约为AS侧的一半.     

Simulation of the mechanical properties of an aluminum matrix composite using X-ray microtomography

Aluminum-based particulate-reinforced metal matrix composites (PMMCs) frequently have a heterogeneous distribution of reinforcement particles whether produced by a powder or liquid processing route. The applicability of X-ray microtomography (XMT) for the characterization of this heterogeneity, and its influence on final properties, was investigated for the case of a powder blended and extruded AA2124 matrix with Ni particulate. Three-dimensional image analysis techniques were used to quantify the embedded Ni particle size distribution and the extent and texture of clusters formed. The XMT data were exploited as a rapid method to generate a microstructurally accurate and robust three-dimensional mesh for input for finite-element modeling. Simulation of the elastoplastic response of the material showed excellent correlation with experimental results. This article is based on a presentation made in the symposium “Computational Aspects of Mechanical Properties of Materials,” which occurred at the 2005 TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA, under the auspices of the MPMD-Computational Materials Science & Engineering (Jt. ASM-MSCTS) Committee.     

粉末冶金结合热轧制备高硼铝合金组织与性能研究

采用粉末冶金结合热轧成形工艺制备含硼质量分数为7%与12%的中子屏蔽用高硼铝合金（Al-7% B与Al-12% B）,并对不同工艺条件下铝硼合金的组织与性能进行研究。结果表明:在机械球磨5 min+放电等离子烧结条件下,Al-7% B合金中AlB₂体积分数高于Al-12% B合金,且分布更加均匀。放电等离子烧结后进行热轧有利于提高试样的相对密度,减少硼粉团聚。在450℃固溶处理2 h,Al-7% B合金试样的拉伸强度和屈服强度达到峰值,分别为145.7 MPa和99.4 MPa。由10B面密度理论计算结果可知,厚度相近时,热轧后高硼铝合金10B面密度均可达到BoralTM水平。     

Structure and properties of a layered steel/vanadium alloy/steel composite prepared by high-pressure torsion

The microstructure and hardness of a layered steel 08Kh17T/V–10Ti–5Cr/steel 08Kh17T composite, which was prepared by torsion under a high hydrostatic pressure at temperatures of 20, 200, and 400°C, have been studied. Severe plastic deformation under used conditions is shown to provide good joining of layers, which is accompanied by their substantial hardening (from 2.0 to 3.5 times). During deformation at temperatures of 20 and 200°C, fragmentation of the vanadium alloy layer into thinner layers is observed; at 400°C, mainly a plane interface between the vanadium alloy and the steel layers is formed.     

硅含量对喷射成形铝硅复合材料显微组织与力学性能的影响

利用双喷嘴扫描喷射成形技术制备27%SiAl、42%SiAl、50%SiAl等3种Si-Al合金电子封装材料,并对该材料进行热等静压致密化处理。研究合金沉积态和热等静压态的显微组织,测定合金的热膨胀系数、抗拉强度及抗弯强度,利用扫描电镜研究其断裂机制。结果表明:沉积态Si-Al合金的硅相呈均匀弥散分布。随含硅量增加,合金凝固区间增大,初生硅相的数量增多,平均尺寸增大,由全部颗粒状分布逐渐演化为呈部分颗粒、部分骨架状分布,这种均匀弥散分布的结构有利于降低合金的热膨胀系数。27%SiAl、42%SiAl、50%SiAl合金的热膨胀系数连续可控,室温至200℃分别为14.76×10 6、9.75×10 6、9.29×10 6/K。随硅含量升高,材料的抗弯强度和抗拉强度呈下降趋势。27%SiAl合金的平均抗拉强度和抗弯强度分别达到196 MPa和278 MPa,伸长率为9.5%。42%SiAl与50%SiAl的平均抗拉强度与抗弯强度都接近,分别达到140 MPa及220 MPa,伸长率小于1%。断裂方式由以铝相的韧性断裂为主逐渐转变为以硅相的脆性裂为主。