Microstructure of Zn-2%Cu Alloy Under Laser Rapid Melting—Solidification

利用5kW连续波CO2激光器对Zn-2％Cu包晶合金进行了表面快速熔凝实验研究，扫描速率从6mm／s至1207mm／s．随着凝固速率的提高，该合金微观组织形态由低速平界面向层片状组织、浅胞晶直至高速绝对稳定平界面转变．实验结果表明，该合金微观组织演化规律与利用林鑫等的数值模型和Jackson—Hunt的共晶模型相结合所得到的界面响应函数作出的预测结果吻合较好．     

Microstructure Evolution and Mechanical Behavior of Laser Melting Deposited TA15 Alloy at 500℃ under In-Situ Tension in SEM

TA15 alloy fabricated by laser melting deposition was investigated at 500℃ under tensile deformation. The damage behavior of microstructure was analyzed by the real time observation of the microstructure evolution, microcracks initiation and propagation using in-situ tensile equipment fitted in the SEM chamber. Finally, the mechanism of fracture was discussed. The result showed anisotropic mechanical properties in X-and Z-direction. The existence of columnar β grains and its orientation to the tensile direction were the major factors inducing the anisotropic mechanical properties. As compared to Z-direction specimen, high tensile strength was observed in X-direction specimen due to the resistance in slips propagation provided by the prior-β grain boundaries( β GBs). Accumulation of the cracks at prior β GB caused the shear fracture. In case of Z-direction specimen, parallel orientation of prior β GB and GB α with the tensile direction resulted in a homogeneous deformation. The high reduction of cross section showed the enhanced ductile characteristics at high temperature.     

Effect of Heat Treatment on the Wear Properties of Selective Laser Melted Ti–6Al–4V Alloy Under Different Loads

As is well known, titanium alloy precipitates when subjected to aging treatment, which poses great influence on its mechanical properties. Thus, solution and solution-aging treatments were conducted in this work, and the wear performance was investigated under diff erent normal loads. The results showed that acicular α ′ martensite in the original selective laser melted Ti–6 Al–4 V was decomposed into α + β phases after the solution treatment, and then Ti₃Al nanoparticles clusters wer...     

Enhanced Strength and Corrosion Resistance of Mg–2Zn–0.6Zr Alloy with Extrusion

The microstructure, mechanical properties and corrosion behavior of Mg–2 Zn–0.6 Zr alloy under the as-cast and asextruded conditions were investigated. Microstructure analysis indicated the remarkable grain refinement by extrusion, as well as notable reductions in volume fraction and size of precipitate phases. As compared with the as-cast alloy, the asextruded alloy exhibited better mechanical performance, especially in yield strength which was promoted from 51 to 194 MPa. Refined grains, dispersive precipitate phases and texture were thought to be the main factors affecting the improved performance in strength. The electrochemical measurement and immersion test revealed the corrosion rate of Mg–2 Zn–0.6 Zr alloy by extrusion decreased from 1.68 to 0.32 mm/year. The reasons for the enhanced corrosion resistance were mainly attributed to the decreased volume fraction and Volta potential of the precipitate phases, the refinement of the grain size, as well as the formation of more protective corrosion film.     

Effect of HIP Treatment on Fatigue Crack Growth Behavior of Ti–6Al–4V Alloy Fabricated by Electron Beam Melting

The effect of hot isostatic pressing treatment on the fatigue crack growth behavior of Ti–6Al–4V alloy fabricated by electron beam melting was investigated.The results indicate that the fatigue crack growth rate of the HIPed samples is higher than that of the as-fabricated one under certain stress intensity factor(DK\18 MPa m~(1/2)).With further increase in DK,the fatigue crack growth rates of the studied two samples become similar.The variation of a lamella thickness and the pore defects distribution have an effect on the fatigue crack growth rates in the studied samples,and the latter plays the dominant role.     

Enhancement of Mechanical Properties of Extruded Mg–9Al–1Zn–1MM–0.7CaO–0.3Mn Alloy Through Pre-aging Treatment

The effect of pre-aging treatment before extrusion has been investigated in Mg–9.0Al–1.0Zn–1MM–0.7CaO–0.3Mn alloy. The as-cast microstructure consists of α-Mg dendrite with secondary solidification phase particles, (Mg, Al)₂Ca, β-Mg₁₇Al₁₂ and Al₁₁RE₃ at the inter-dendritic region. After extrusion, β-Mg₁₇Al₁₂ precipitates are present, but higher density and more homogeneous distribution in pre-aged alloy. In addition, μm-scale banded bulk β-Mg₁₇Al₁₂ particles are generated during extrusion. Al₁₁RE₃ particles are broken into small particles, and are aligned along the extrusion direction. (Mg, Al)₂Ca particles are only slightly elongated along the extrusion direction, providing stronger particle stimulated nucleation (PSN) effect by severe deformation during extrusion. The mechanical properties can be significantly enhanced by introducing pre-aging treatment, i.e. β-Mg₁₇Al₁₂ precipitates provide grain refining and strengthening effects and (Mg, Al)₂Ca particles provide PSN effect.     

Improvement of Oxidation Behavior of a Ti–48Al–2Cr Alloy by a Nitridation Treatment

The effect of a nitridation treatment for 10 hr at 800°C on the oxidation resistance of a Ti–48Al–2Cr (at.%) alloy in air at 800°C was evaluated. Results prove that nitridation decreases by about 40% the total mass gain of nonnitrided material, although the oxidation mechanism is the same for both materials. The oxidation can be divided into two stages. The formation of a nonprotective mixed alumina–rutile scale during the transient stage results in a high oxidation rate. A further decrease in the oxidation rate arises from the establishment of an external alumina-rich layer during the steady stage. The main difference between the scale developed on both materials is the continuous nature of the nitride layer present in the nitrided material during the entire exposure. The thin continuous nitride layer formed during the nitridation treatment acts beneficially as a diffusion barrier, preventing oxygen dissolution in the ₂-Ti₃Al phase during the transient stage. Furthermore, the oxygen gradient through the oxide scale is kept low, because no oxygen is removed at the scale–alloy interface.     

Effect of Surface Polishing Treatment on the Fatigue Performance of Shot-Peened Ti–6Al–4V Alloy

In this study, shot peening is applied to the titanium alloy Ti–6Al–4V, and the surface treatment effect on fatigue life of shot-peened specimens under high cycle loading is investigated. The induced residual stress is measured by using the orbital hole-drilling method. Surface profilometer and optical microscopy are employed to characterize the surface roughness and morphology. The deformed microstructure layers of the shot-peened specimens are investigated by using scanning electron microscopy. Experiments reveal that the fatigue life of Ti–6Al–4V is improved by the shot peening process, and the surface pre-peening polishing. The combination of pre-and post-peening polishing treatments further improves fatigue life of Ti–6Al–4V specimens. The present work provides useful guidelines for developing more efficient shot peening strategies.     

Orientation Dependence of the Micro-Pillar Compression Strength in an Electron Beam Melted Ti–6Al–4V Alloy

An α/β two-phase Ti-6 Al-4 V alloy was fabricated by electron beam melting to obtain a basketweave structure.The orientation dependence of the mechanical properties of Ti-6 Al-4 V alloy was studied by micro-pillar compression and post-mortem transmission electron microscopy analysis.The results indicate that different grains have different mechanical responses,and the possible attributions were discussed.Besides the orientation effect,due to the limited volumes of micropillars,the size of the a phases,dispersion of the β phases,and the presence of the free dislocation path also affect the mechanical properties of the micropillars to a large extent.Although no direct link was discovered between the mechanical properties and the parent βorientations,this work provided a promising method to further study the anisotropic mechanical behavior in Ti-6 Al-4 V alloy.     

Microstructure Evolution and Phase Transformation of Ti–6.5Al–2Zr–Mo–V Alloy During Thermohydrogen Treatment

Thermohydrogen treatment(THT) is an effective way to refine microstructure and improve the mechanical properties of the titanium alloys.In the current work,as-cast Ti–6.5Al–2Zr–Mo–V alloy was hydrogenated with different hydrogen contents and processed solution aging.Accordingly,the microstructure evolution and phase transformation were analyzed.Results show that during solution aging,eutectoid decomposition occurs and the product is a mixture of coarse primary a,fine eutectoid product and undecomposed bH.The size of primary a is closely dependent on the hydrogen content,and large primary a can be obtained at medium hydrogen content.Further,the influence of hydrogen content on the growth of primary a phase was revealed.The primary a is much fine,and the eutectoid product is relatively homogeneous with 0.984 wt% H.After THT,the ultimate strength is beyond 1,100 MPa that has increased by 23.15% compared with that in as-cast state.     

热处理对激光熔化沉积18Ni300马氏体时效钢微观组织和力学性能的影响

目的 提高18Ni300马氏体时效钢在工业应用中的力学性能,研究不同热处理对激光熔覆制备18Ni300合金的影响。方法 采用固溶处理(840℃/1 h)和固溶处理(840℃/1 h)+时效处理(490℃/6 h)2种热处理方法,利用扫描电子显微镜、X射线衍射仪和拉伸试验机对激光熔化沉积(LMD)制备18Ni300合金的微观组织、力学性能进行研究,根据不同处理方法下的拉伸断口形貌、性能表征及元素偏析行为,分析热处理对力学性能的影响。结果 经固溶处理后,熔池边界消失,在高温保温过程中杂质相与合金元素充分溶解在奥氏体中,冷却后形成了均匀的马氏体组织,与沉积态相比,抗拉强度由662.1 MPa变为611.5 MPa,降低了约7.64%,伸长率由12.328%变为13.832%,提升了约12.20%;经固溶+时效处理后枝晶形貌基本消失,各元素分布均匀,并在基体中弥散分布着Ni₃Mo、Ni₃Ti型第二相沉淀,抗拉强度达到1 404.6 MPa,提升了约112.14%,伸长率为7.80%,降低了约36.72%,在断口中观察到亚微米级第二相沉淀呈球状或颗粒状...     

激光熔化沉积300M超高强度钢的显微组织

利用OM和SEM分析了激光熔化沉积快速成形300M钢薄板的显微组织,测试了硬度随沉积高度的变化规律.结果表明:薄板状试样具有细小、均匀的胞状树枝晶组织,其显微组织随沉积高度增加变化显著,底部为贝氏体及马氏体回火组织,中、下部为无碳化物贝氏体 岛状马氏体/奥氏体(M-A)组织,中、上部为马氏体和贝氏体的混合组织;试样宏观硬度沿沉积增高方向呈台阶状变化,3个硬度平台区分别对应于上述3种不同的显微组织.试样显微组织及硬度随沉积高度的变化是由于激光熔化沉积过程中不同沉积高度处的材料经历的快速非稳态热循环历史不同,从而发生不同的固态相变过程所致.     

45钢激光熔凝的组织与性能研究

采用TJ-HL-T5000型连续横流CO2激光器对45钢表面进行激光熔凝处理.通过熔凝后的组织和性能变化,研究了熔凝处理对45钢的影响.结果显示,表面熔凝后的组织受固溶强化、位错强化和细晶强化等强化作用,使材料机械性能显著提高.     

镁合金激光表面处理技术的应用

激光加工技术是近几十年来迅速发展起来的一门高新技术.综述了激光表面改性技术在镁合金上的研究与应用.探讨了激光表面处理技术在镁合金中应用的发展趋势和广阔前景.     

激光直接沉积TC11/TC17双合金的组织及性能

研究了直接连接及梯度连接两种激光直接沉积TC17/TC11双合金的显微组织及力学性能。结果表明,两种连接方式成形的TC17/TC11双合金均可分为TC17均一成分区、过渡区及TC11均一成分区三个区域,沉积态下,两种连接方式均一成分区显微组织呈层带状周期分布;直接连接TC17/TC11双合金过渡区极窄,两侧化学成分、显微组织在交界处发生突变;梯度连接TC17/TC11双合金过渡区厚度较大,过渡区化学成分呈连续过渡,显微组织受成分变化和热循环双重影响,呈介于TC17和TC11中间态显微组织;直接连接过渡区显微硬度存在突变,梯度连接过渡区显微硬度由TC17侧逐渐过渡至TC11侧;直接连接和梯度连接样品室温拉伸断裂位置均在TC11均一成分区,强度接近,延伸率分散度较大。     

激光熔化沉积法制备2A50铝合金热处理工艺研究

基于激光熔化沉积技术进行了高强度锻造型2A50铝合金增材制造实验,为了提高增材构件的综合力学性能,开展了增材制造高强度铝合金的热处理工艺研究。结合X射线衍射分析仪(XRD)、扫描电子显微镜(SEM)、显微硬度仪以及拉伸试验等检测手段,研究了不同热处理工艺参数对增材试样微观组织及力学性能的影响规律。结果表明：沉积态试样具有明显的柱状树枝晶结构,热处理后粗大柱状树枝晶发生断裂,晶粒开始球化并在晶界处形成均匀分布的块状第二相;在优化的热处理工艺条件下(540 ℃×1 h+150 ℃×16 h),结合溶质元素的固溶强化与第二相的析出强化作用,增材试样的屈服强度、抗拉强度、显微硬度的平均值分别由沉积态的90.7 HV、85 MPa、207 MPa提高至热处理后的137.2 HV、245 MPa、321 MPa。     

强冷T8钢激光熔凝处理的研究

研究了室温和强冷（－１９６℃）Ｔ８钢激光熔凝处理后的组织和性能．结果指出，强冷基体使熔池尺寸变小，熔池中奥氏体晶粒细化，表面显微硬度及硬度梯度峰值提高．     

激光熔凝处理H13钢的组织和性能

采用光学金相、SEN和XRD等方法研究了经激光熔凝处理的H13钢的显微组织，并对其性能进行了测试。结果表明，其剖面组织分为熔凝区、热影响区和基体三个部分。熔凝区组织为马氏体和残余奥氏体，合金元素基本均匀分布，晶粒超细化。与常规热处理相比，其硬度、耐磨性和回火稳定性显著提高。     

Selective Laser Melting of 30CrMnSiA Steel: Laser Energy Density Dependence of Microstructural and Mechanical Properties

Three-dimensional parts of the 30 CrMnSiA steel were successfully fabricated using selective laser melting(SLM). The microstructures and mechanical properties of the SLM-processed 30 CrMnSiA samples were investigated by scanning electron microscope and transmission electron microscopy. The results indicate that the microstructures of the 30 CrMnSiA samples consist mainly of lath martensite and acicular martensite. The value of the surface roughness decreases with increasing laser energy density(LED) before it reaches a minimum and then increases with further increasing LED. The relative density, microhardness and ultimate tensile strength of the SLM-processed samples initially increase and then decrease with increasing LED. By taking the relative density, surface roughness, microhardness and ultimate tensile strength into account, the optimized LED should be in the range of 46.15–51.28 J mm~(-3) for the SLM-processed30 CrMnSiA alloys. In addition, the differences in the microstructures and mechanical properties between the conventionally wrought 30 CrMnSiA sample and SLM-processed 30 CrMnSiA samples were also studied.     

激光熔凝处理对P20钢组织及性能的影响

目的 提高P20模具钢的表面硬度和耐磨性能。方法 采用激光熔凝技术对P20模具钢表面进行强化处理。通过硬度梯度检测和摩擦磨损测试,分别评价熔凝层的硬度分布特征和耐磨性能,并通过光学显微镜和扫描电子显微镜对熔凝层及磨痕形貌进行分析。结果 使用激光输出功率为500 W、光斑直径为2.5 mm、聚焦透镜距离为40 mm、扫描速度为6 mm/s、搭接率为45%、氮气保护的激光熔凝工艺所得熔凝层的组织细小,无脱碳、畸变、裂纹等缺陷,熔凝处理质量高。熔凝过程中单道激光熔凝层呈半椭圆形分布,最大深度为610～620μm。熔凝处理后表面硬度提升显著,熔凝层的硬度分布与熔凝层的区域位置有关,具有较高硬度且硬度保持基本稳定的熔凝层深度约为400μm;单道激光熔凝层最高硬度可达460～480HV,重叠影响区即双熔凝区的最高硬度在540～560HV之间,即熔凝层硬度普遍较基体硬度提高了60%以上。此外,P20模具钢经过激光熔凝处理后耐磨性能提升明显,其平均摩擦因数约为0.85,熔凝处理的磨损失重较未处理的试样减少了约61%,其磨损机制主要表现为磨粒磨损和少量的黏着磨损或剥落脱离。结论 激光熔凝处理能够显著提高...