超声磨削氧化锆陶瓷表面相变与残余应力特征实验研究

针对氧化锆陶瓷的易相变特点,通过对ZTA陶瓷和纳米氧化锆陶瓷进行对比实验,研究了氧化锆陶瓷磨削表面相变特性,分析了磨削表面的残余应力特征.实验结果表明,亚稳态四方相氧化锆的含量以及磨削应力是诱发氧化锆陶瓷产生马氏体相变的主要因素;陶瓷磨削过程中,砂轮的磨削深度越大、磨粒粒径越大,在材料基体中产生的磨削应力越大,从而马氏体相变率增大;纳米氧化锆陶瓷磨削表面产生的残余压应力值大于ZrO2增韧Al2O3(ZTA)陶瓷.通过分析磨削参数对残余应力的影响,验证了马氏体相变可在一定程度上促进残余压应力的产生,从而提高磨削表面的质量.     

超声振动磨削纳米氧化锆陶瓷材料的磨削力及表面残余应力的研究

纳米陶瓷由于其相对于工程陶瓷优越的力学性能及物理特性,在各行业都有广泛的应用前景。采用超声复式加工方法,针对不同的磨削参数对纳米ZrO2陶瓷进行了普通和超声磨削实验,研究了磨削参数对磨削力的影响,并通过X射线衍射分析了在普通和超声磨削状态下对工件表面残余应力及纳米ZrO2陶瓷各晶相的影响。研究结果表明:利用超声振动磨削能有效减少磨削力,不同的磨削方式对纳米ZrO2陶瓷表面残余应力影响较大,采用普通磨削工件表面残余应力为拉应力,当超声振动方向平行于砂轮速度方向时,工件表面残余应力为压应力,振动方向垂直于砂轮速度方向时工件表面残余应力绝对值较小。     

陶瓷结合剂CBN砂轮磨削钛合金的研究

本文研究了陶瓷结合剂CBN砂轮磨削钛合金的磨削力特征、砂轮磨损特征以及磨削表层的残余应力分布等。研究结果表明,采用陶瓷结合剂CBN砂轮磨削钛合金,不仅磨削比高,磨削力、摩削温度低,而且磨削零件表面可获得残余压应力。     

工程陶瓷超精密磨削表面质量的研究

本文从几何和物理特性两方面研究了ZrO2和Sialon陶瓷超精磨制削的表面质量。实验结果表明：金刚石砂轮磨粒尺寸和磨削深度对磨削表面的微观形貌如几何形态和表面纹理具有重要影响。超精密磨削的表面存在着残余应力，但其数值较小，残余应力从表面向材料内部迅速减小，砂轮磨粒尺寸和磨削深度是残余应力的主要影响因素。在ZrO2和Sialon陶瓷超精密加工的表面上亦存在着相变，ZrO2陶瓷的相变将引起表面残余压应力的增加，Sialon陶瓷的相变对表面残余应力的影响很小，采用TEM和XRD对超精密磨削表层结构的研究表明，在加工表层存在着很深的变质层，它由表面的非晶层和相邻的塑性变形层组成，然后逐步过渡到基体组织。     

表面抛光对工程陶瓷磨削断裂强度的影响规律

断裂强度受到磨削表面微观形貌和残余应力场分布的影响。对Si3N4、SiC和Al2O3陶瓷材料实施平面磨削后,用金相显微镜、表面轮廓仪和X射线应力测试仪研究陶瓷机械抛光前后表面微观形貌、粗糙度、残余应力与工件磨削断裂强度的关系。结果表明:经无水乙醇润滑抛光后SiC陶瓷具有平滑的表面微观形貌、较低的表面粗糙度和残余应力;反应烧结的Si3N4、SiC和Al2O3陶瓷磨削并抛光20min后的断裂强度幅度依次为6.64%、8.18%和6.58%;适当的抛光时间能降低陶瓷磨削表面应力集中程度及残余拉应力,使陶瓷的断裂强度得到一定提升。     

氮化硅陶瓷的残余应力和抗弯强度特性

利用X射线衍射方法测量了经不同磨削的氮化硅陶瓷表面残余应力及其对抗弯强度的影响。结果表明 ,磨削工艺所引入的残余应力是拉应力 ,显著降低陶瓷抗弯强度。     

20CrMnTi磨削表面质量试验研究

为了探讨磨削工艺参数对20CrMnTi磨削表面质量的影响,采用CBN砂轮开展单因素磨削试验,选取表面洛氏硬度H、表面残余应力σ_s和亚表面残余应力分布σ_ss作为指标,通过试验分析20CrMnTi的磨削加工特性。试验结果表明:相同条件下,H随着砂轮线速度v_s和磨削深度a_p的增大而减小,随着工件进给速度v_w的增大而增大,且a_p的影响最大、v_w的次之、v_s的最小;磨削后工件表面表现为残余压应力,压应力σ_s的大小(绝对值)随着v_w增大而增大,随着a_p增大而减小,随v_s增大呈现波动;磨削后工件的σ_ss随着a_p增大逐渐由压应力转变为拉应力,最后趋于0;在小v_s和较小a_p时,在相同亚表面深度情况下可以获得更大的压应力或者更小的拉应力。在本试验所讨论的参数范围内,v_s=60 m/s,v_w=1.045 m/s,a_p=3 μm时可以获得较高H和残余压应力以及较好的σ_ss,即20CrMnTi磨削加工质量较好。      

磨削用量对42CrMo钢淬硬层残余应力的影响

磨削淬硬是集成表面淬火与磨削加工的制造技术,衡量其表面质量的主要特征参数是残余应力。对42Cr Mo钢进行了平面磨削加工试验,分别研究了磨削速度vs、磨削深度ap、进给速度vw对残余应力σx的作用,初步总结了vs、ap、vw对残余应力的影响规律,揭示了淬硬层残余应力与显微硬度分布之间的关系。试验研究发现,当vs、ap的值增加,vw减少的时候,磨削淬硬层表面残余应力σx的值会随之减少,但最大残余应力和其作用的深度却随之增加。本研究为主动控制磨削淬硬加工质量提供了理论与试验依据。     

以σ_z/σ_t判断砂轮磨损及确定砂轮耐用度的研究

本文通过恒速磨削及恒力磨削条件下砂轮磨损对加工表面质量的影响的系统研究,提出了以工件表面轴向残余应力σ_x与切向残余应力σ_t的比值σ_z/σ_t判断砂轮磨损及确定砂轮耐用度的新方法。试验结果表明,σ_x/σ_t之值的变化与砂轮磨损有很强的对应关系,在砂轮钝化后,σ_z/σ_t之值急剧增大,并产生无规律波动,与目前以表面粗糙度确定砂轮耐用度方法相比,以σ_z/σ_t确定砂轮对角度可获得具有更好的表面完整性的加工工件,且工艺过程稳定。     

氮化硅陶瓷磨削表面残余应力的测试与计算

利用X射线衍射应力分析的sin2 ψ法测量、计算出氮化硅陶瓷试样的残余应力。分析表明 ,经平面磨磨削后的气压烧结氮化硅陶瓷试样表面存在的残余应力为拉应力 ,而再经过表面抛光处理 ,则可以适当地降低表面残余应力。     

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).     

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.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.