激光熔凝强化RuT300收尾参数变化对熔池影响规律的研究

利用ANSYS有限元仿真模拟软件,建立了激光熔凝强化RuT300三维数学物理仿真模型。模型中考虑了材料的相变潜热、热物性参数及激光吸收率的影响,分析了激光熔凝收尾过程中激光功率线性下降及下降速率、激光扫描速度线性上升及上升斜率对熔池形状的影响规律。结果表明:随着激光功率的线性下降或激光扫描速度的线性上升,熔池的面积、深度及宽度均降低;伴随激光功率线性下降斜率绝对值的增大或激光扫描速度线性上升斜率的增大,熔池的面积、深度及宽度均降低。     

预热温度对激光熔凝RuT300气门座残余应力场的影响研究

目的 为了突破激光熔凝蠕墨铸铁RuT300气门座裂纹抑制技术的瓶颈,研究了预热温度对激光熔凝RuT300气门座残余应力场的影响,从而为工程上抑制裂纹的参数优选提供支撑。方法 基于热弹塑性理论,建立了激光熔凝RuT300气门座残余应力场分析的数学物理模型,模型中考虑了预热温度、激光熔凝参数、材料性能参数的变化对残余应力的影响。结果 预热温度对激光熔凝RuT300气门座残余应力场的影响与熔池冷却速度、峰值温度等密切相关：当预热温度在25~150 ℃时,随着预热温度的升高,冷却速度下降对激光熔凝RuT300气门座热膨胀变形引起的应力降低起主要作用,导致气门座环向残余应力值随预热温度的升高而减小;当预热温度在150~250 ℃时,随着预热温度的升高,峰值温度上升诱发的热膨胀变形加剧所引起的应力增加起主要作用,导致气门座环向残余应力值随预热温度的升高而增大。结论 预热温度的变化影响气门座的冷却速度和峰值温度,而残余应力值的变化是气门座冷却速度和峰值温度等综合影响的结果,通过合理的调控预热温度,可以使激光熔凝RuT300气门座的残余应力值降低到最低,从而减小气门座激光熔凝形成裂纹的倾向。     

RuT300气门座激光熔凝温度场数值模拟

建立了激光熔凝气门座的数学物理模型,模型中考虑了材料的热物性参数随温度的变化及材料的相变潜热。结果表明:随激光功率的增加,激光熔凝气门座熔池最高温度升高,且激光熔凝区的深度和宽度增加;随激光扫描速度的提高,激光熔凝气门座的最高温度下降,且熔凝区的深度和宽度减小;随激光光斑半径的增加,激光熔凝气门座的最高温度降低,激光熔凝区深度减小。激光熔凝气门座过程是新熔池形成和已形成的熔池凝固二者同步的过程,由于不同区域温度分布和冷却速度等差异,导致气门座表面熔池形态为彗星拖尾状;且彗星拖尾状随激光功率的增大而增加,彗星拖尾状随扫描速度和激光半径的增加而降低。随激光半径的增加,熔池彗星拖尾的尖形曲率减小。实验与数值模拟结果基本吻合,这说明了模型的有效性。     

激光参数对蠕墨铸铁熔凝组织演变及高温力学性能的影响

采用额定功率为3 kW的Nd:YAG激光器开展不同激光参数的激光熔凝蠕墨铸铁试验,通过扫描电镜、光学显微镜、硬度仪和高温加热炉表征了激光熔凝宏观形貌、微观特性变化、硬度分布和高温回火性能。结果表明:由于激光熔凝蠕墨铸铁中匙孔效应及不同激光参数差异等影响,熔凝区宏观形貌呈现勺形、帽形、碗形和盆形;伴随激光功率的增加和扫描速度的降低,且激光功率密度达到形成匙孔能量密度阈值时,熔凝区域的深宽比增加;伴随激光扫描速度和侧吹保护气流量的增加,熔凝区网状莱氏体分布区域减少;随着激光功率的增加,熔凝中心区域莱氏体由层片状转变为网状;对激光熔凝蠕墨铸铁进行500℃回火工艺处理,熔凝区硬度增加,基体与热影响区硬度降低。     

45钢光纤激光熔凝工艺

采用光纤激光对45钢表面进行了激光熔凝处理研究. 结合熔凝层深度、组织、显微硬度和摩擦磨损性能分析,研究了多道激光熔凝的激光功率、激光扫描间距对熔凝工艺的影响规律. 结果表明,在改变激光功率的研究中,熔凝层深度随激光功率的增大而增加,熔凝层的显微硬度呈周期性变化,后道激光处理对前道熔凝层存在回火热处理作用. 在改变激光扫描间距的研究中,进一步验证了后道激光熔凝对前道的热影响作用,同时适当增大扫描间距,获得软硬相间的熔凝层表面,有利于改善钢材表面的耐磨性能,同时可适当提高激光熔凝处理的生产效率.     

Ni60/WC涂层表面圆凹坑皮秒激光加工关键参数研究

目的 优化激光路径填充方式以减少皮秒加工圆凹坑底部的堆积现象,并探究基于该激光路径填充方式的皮秒激光关键参数对Ni60/WC涂层表面圆形凹坑形貌参数的影响规律。方法 采用搭建的紫外皮秒激光微加工平台在Ni60/WC涂层表面加工预先规划的直径为230μm的圆凹坑,通过白光干涉仪测试加工所得圆凹坑的整体三维形貌对圆凹坑底部形貌进行表征。采用同心圆网格复合激光路径填充方式对圆凹坑底部堆积现象进行优化,并通过单因素法分析该路径下皮秒激光关键参数,即加工功率、扫描次数、扫描速度对圆形凹坑深度、直径和圆度系数的影响规律。结果 通过优化的同心圆网格复合激光路径填充方式加工所得圆凹坑材料去除体积为7.59×10⁶μm³,轮廓算术平均高度为21.37μm,对比原始的网格激光路径填充方式,加工的圆凹坑底部无明显堆积;基于此激光路径填充方式,在测试工艺参数范围内,圆凹坑深度、直径和圆度系数随激光功率的增大呈二次函数增大;随着扫描速度的增大,圆凹坑深度、直径呈线性减小,圆度系数呈线性增大;圆凹坑深度、直径和圆度系数随扫描次数的增加均呈线性增大。结论 同心圆网...     

光纤激光-渗氮处理对Cr12MoV钢组织和性能的影响

采用IPG的YLS-3000型光纤激光器对Cr12Mo V钢表面进行原位激光-渗氮处理。通过光镜、扫描电镜、X射线衍射及金相显微硬度计,分析研究不同激光处理参数对渗氮层组织及性能的影响。结果表明,在扫描速度和离焦量一定的条件下,Cr12Mo V激光熔凝层深度随激光功率的增加而增大,激光渗氮处理可使材料表面显微硬度提高。Cr12Mo V钢激光渗氮后的组织由熔凝区、热影响区及基体三部分组成。随着激光熔凝速度的增大,熔凝区树枝晶逐渐变得细小。随着激光熔凝功率的增加,熔凝区树枝晶逐渐变得粗大。熔凝层的硬度峰值出现在距材料表面1.0 mm附近,两侧呈对称降低,硬度峰值则随激光功率的增加而增加。     

AZ91HP镁合金真空激光熔凝晶粒细化

采用真空激光熔凝技术对AZ91HP镁合金表面进行了细晶强化处理。研究表明：激光熔凝区是由α-Mg和β-Mg17Al12相所组成,与原始镁合金相比,β-Mg17Al12相含量增加,且随着激光扫描速度降低,β-Mg17Al12相含量增加。熔凝区具有典型的树枝晶形貌特征。由于受微区合金溶液成分和结晶参数不均匀性的影响,二次枝晶间距沿熔凝层深度逐渐增大。增加扫描速度导致熔凝区二次枝晶间距减小,激光熔凝区晶粒细化,有利于提高镁合金的塑性。     

激光选区熔化WC 12Co复合材料温度场模拟研究北大核心CSCD

为提高激光选区熔化WC 12Co硬质复合材料的成形质量,采用有限元仿真软件Ansys 2021R1对SLM成形WC 12Co硬质复合材料过程的温度场进行数值模拟仿真研究,研究成形温度场的温度分布和成形工艺参数(激光功率、扫描速度、扫描间距和基板预热温度)对温度场的影响,为优化WC 12Co硬质复合材料成形提供试验依据。结果表明:激光功率增大,成形区域温度增大,位置点3的峰值温度从3507.47℃增大至3837.52℃;激光扫描速度增大,成形区域温度降低,位置点5的峰值温度从3592℃下降至2897℃,峰值温度下降695℃;扫描间距的增加使各扫描区域的温度有所降低,位置点3的峰值温度从3330℃逐渐降低至3123℃。在同一成形工艺参数下,激光扫描前一路径对后一路径有预热作用,随着扫描路径的增加,成形区域的温度呈现逐渐上升趋势。基板预热至120℃能够提高熔池的内部温度,减小成形件之间的温度差异,缩小温度梯度差。当激光功率增大时,熔池的宽度和深度随之增大;当激光扫描速度增大时,熔池的宽度先增大后减小,熔池的深度线性反向减小;当扫描间距增大时,熔池的宽度和深度均减小。模拟获得的温度场仿真结论能够大致反映成形试样的表面质量和合金粉末的熔化状态随成形工艺参数变化的趋势。     

TC11钛合金表面微凹坑织构皮秒激光加工工艺

目的研究皮秒激光加工工艺参数对微凹坑形貌的影响规律。方法采用FSLAB-50-05激光器搭建的激光器平台对TC11钛合金工艺试样进行表面微加工,通过WYKO—NT1100型表面三维形貌测试仪获得表面微凹坑织构形貌,分别记录微加工后的二维与三维形貌图,应用单因素法分析激光重复频率、激光持续时间和激光功率对微凹坑形貌的影响规律。结果在激光功率为10 W、激光持续时间为0.12 ms的前提下,当激光重复频率由50 k Hz增加到250 k Hz时,微凹坑的直径和深度均呈现出先增大后减小的趋势;在激光功率为10 W、激光重复频率为300 k Hz的前提下,当激光持续时间由0.02 ms增加到0.10 ms时,微凹坑直径和深度均随着激光持续时间的增加而变大;在激光重复频率为300 k Hz、激光持续时间为0.12 ms的前提下,当激光功率由4 W提升至12 W时,微凹坑的深度随着激光功率的增大而增大,而宽度先增大后减小。结论皮秒激光微凹坑织构较佳的工艺参数范围为:激光重复频率150~200 k Hz,激光持续时间0.04~0.06 ms,激光功率8~10 W。     

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.