烧结工艺对ZrO2/Cu纳米复合材料性能及组织的影响

采用原位化学工艺制备了ZrO2/Cu纳米复合粉末,并用粉末冶金法制备了ZrO2/Cu纳米复合材料。研究了烧结温度、烧结时间对纳米复合材料性能的影响。结果表明,随着烧结温度的升高,复合材料的体积收缩率增大,同时电导率、显微硬度也增大;随着烧结时间的延长,体积收缩率增大,显微硬度增大到一定程度后减小。当烧结温度为975℃,时间为90min时,得到的ZrO2/Cu纳米复合材料性能较佳(122HV,93.4IASC%)。     

纳米WC-6%Co复合粉的放电等离子烧结研究

以水溶液化学法制备的WC-6%Co纳米复合粉体为原料,利用放电等离子烧结(spark plasma singtering,SPS)技术制备了超细硬质合金。研究了烧结温度对硬质合金显微组织和力学性能的影响,分析了纳米粉体烧结的致密化过程。结果表明:随着烧结温度的升高,烧结致密性、硬度和断裂韧性都呈现先增加后降低的变化趋势,在升温速度为100℃/min,烧结温度为1 250℃,保温时间5 min,压力为30 MPa的工艺条件下,利用SPS技术可制备综合力学性能良好的超细晶硬质合金,平均晶粒大小为420 nm,维氏硬度为1 969 HV30,断裂韧性为10.7 MPa·m~(1/2)。     

微波烧结工艺对钨基合金挤压棒坯显微组织及力学性能的影响

研究了微波烧结温度和时间对钨基合金挤压棒坯显微组织及力学性能的影响。采用高倍SEM和光学金相显微镜分别对合金断口和显微组织进行了形貌观察;对合金相对密度、抗拉强度、延伸率和硬度进行了测定和分析。结果表明:当微波烧结时间为30min时,随着烧结温度的升高,合金性能呈峰值变化,烧结温度为1550℃时,合金的力学性能达到极大值,相对密度、抗拉强度、延伸率和HRC硬度分别为98.3%、920MPa、9.7%和30.5;当微波烧结温度为1550℃时,随着烧结时间的延长,合金的力学性能先上升后下降;随着微波烧结温度的升高及微波烧结时间的延长,钨晶粒的尺寸逐渐增大。     

热处理工艺对Cu-Fe-P合金显微硬度及导电率的影响

自行设计了一种Cu Fe P系合金 ,研究了固溶温度、时效温度以及时效时间对该合金显微硬度和导电率的变化规律。结果表明 ,该合金的最佳固溶处理工艺为 90 0℃× 70min ,并在 4 0 0℃× 2h时效条件下具有较好的综合性能 ,显微硬度可达到 10 6 4HV0 1,导电率可达 82 3%IACS。试验结果还表明 ,在 4 0 0℃、5 0 0℃下时效 ,随着时间的延长合金显微硬度会出现两个峰值。     

真空烧结温度对Cu-Al-Mn形状记忆合金性能的影响

选择不同的烧结温度,采用粉末冶金的方法制备了Cu- 12Al-2.5Mn形状记忆合金.借助扫描电镜、金相显微镜、能谱仪等设备对比了各种温度下合金的显微组织、硬度及形状记忆性能,得到最佳烧结温度范围.试验结果表明:烧结过程中合金的各元素问产生冶金结合,且合金化程度随温度的升高而增大,最佳烧结温度范围是850～900℃;烧结后合金试样的心部硬度低于边缘部分,850℃和900℃的合金经800℃保温10 min水淬后硬度均匀,硬度值较高,分别为HRB42.5和HRB52; 850℃的合金形状记忆性能优于900℃的合金.     

烧结温度对M3∶2高速钢SPS烧结组织和性能的影响

采用放电等离子烧结技术(SPS)制备了M3∶2粉末冶金高速钢,研究了SPS烧结M3∶2粉末冶金高速钢最佳烧结温度、显微组织与性能.通过实验得到以10℃/min的速率升到1200℃时高速钢的连续升温烧结曲线,分析在此烧结实验下的烧结过程,进而确定烧结温度范围.在此范围内的不同温度下烧结试样,根据试样密度、硬度、相对密度和显微组织确定M3∶2粉末高速钢最佳烧结温度.结果表明:在烧结温度900℃、保温时间10min、压力30 MPa工艺下,SPS烧结的M3∶2粉末冶金高速钢,其显微组织均匀、晶粒细小、无碳化物偏析,相对密度达98.17％,硬度达63.37 HRC.     

含钪Al-Zn-Mg-Mn-Zr合金时效制度

采用铸锭冶金方法，制备了Al-6．2Zn-2．3Mg-0．3Mn-0．25Sc-0．12Zr合金。利用室温拉伸、硬度测试方法，透射电子显微分析方法研究了Al-6．2Zn-2．3Mg-0．3Mn-0．25Sc-0．12Zr合金在不同时效条件下的力学性能、显微组织结构。结果表明，Al-Zn-Mg-Sc-Zr合金在100℃、120℃、140℃、160℃下时效，在同一温度下，随着时效时间的延长，合金硬度逐渐上升，在达到时效峰值后逐渐降低，均具有明显的时效硬化特性；随着时效温度的升高，合金达到时效硬度峰值的时间缩短，但相应的时效硬度峰值减小。     

金刚石抛光用钨合金的热压烧结

为了获得适用于摩擦化学抛光单晶金刚石用的高性能W-Mo-Cr合金抛光材料,采用机械合金化法制备的微细W-Mo-Cr合金粉末为原料,研究热压烧结参数(烧结温度、压力和保温时间)对材料致密度和硬度的影响,并采用扫描电镜(SEM)对材料的显微组织进行观察。结果表明:采用机械合金化和热压固相烧结相结合的方法可以制备出高致密度、高硬度的合金材料,合金材料组织致密,平行精度良好;在烧结温度为1400℃、压力为30 MPa、保温时间为30 min的工艺条件下,所制备的W-Mo-Cr合金材料相对密度为96.49%,硬度为777.78HV。     

Mg-12Li-2Al-2Zn合金化学镀镍工艺的研究

研究化学镀液pH值、温度及施镀时间对Mg-12Li-2Al-2Zn合金表面镀镍层组织形貌和性能的影响.结果表明:在镁锂合金表面进行化学镀镍的最佳工艺参数是:pH=7±0.2,温度(80±2)℃,施镀时间50 min.在此工艺条件下,所获镀层厚度13～15μm,显微硬度435 HV左右,镀层结构为Ni-P非晶态.     

放电等离子烧结TA15钛合金及石墨烯增强TA15复合材料微观组织与力学性能

采用放电等离子烧结(SPS)方法制备了TA15钛合金,并研究了烧结温度、烧结时间以及烧结压力参数对合金致密化、微观组织与力学性能的影响.结果表明:在烧结温度为800～1200℃、烧结时间为3～7 min、烧结压力为20～50 MPa的烧结条件下,烧结参数对TA15钛合金的物相组成影响不大;合金的微观组织主要由烧结温度决定,并且延长烧结时间会使微观组织发生一定的粗化,而烧结压力对微观组织没有明显的影响.升高烧结温度、延长烧结时间以及适当地增加烧结压力,有助于TA15钛合金致密化过程的进行.烧结态TA15钛合金的室温及高温压缩力学性能由合金的致密度和微观组织共同决定.采用SPS工艺在900℃及50 MPa的烧结条件下,5 min即可获得致密的TA15钛合金,并具有最佳的室温及高温综合力学性能.此外,在900℃、50 MPa和7 min的烧结条件下,采用SPS制备了0.5％(质量分数)石墨烯增强TA15复合材料,与TA15钛合金相比,复合材料室温与高温压缩屈服强度及极限抗压强度得到了明显提高.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.