不同路径对电子束熔丝沉积304不锈钢组织与性能的影响

目的 采用电子束熔丝沉积方法进行打印,以获取具有高抗拉强度与高伸长率的304不锈钢。方法 以304不锈钢丝材为材料,当加速电压为60kV、聚焦电流为430m A、束流强度为22m A、成形速度为250 mm/min、送丝速度为1 400 mm/min时,在成形路径为“弓字形”和“交替弓字形”条件下打印不锈钢样品,在样品x、y、z 3个方向上截取试样,采用金相、扫描电镜、透射电镜及拉伸试验等分析手段,对试样的微观组织和力学性能进行研究。结果 在“弓字形”成形路径下,产品x方向试样的显微组织主要以等轴晶为主,而y方向试样的显微组织以相互平行的柱状晶为主;在“交替弓字形”成形路径下,产品微观组织主要是相互垂直的柱状晶,在z方向试样中出现了位错胞结构。在“交替弓字形”成形路径下,z方向试样具有最优的综合力学性能,其致密度为98.60%,抗拉强度为（1 344±14）MPa,屈服强度为（701±7）MPa,断后伸长率为（25±0.4）%。结论 在EBF打印304不锈钢样品中,选用“交替弓字形”成形路径能使不锈钢具有更高的致密度,可以提升抗拉强度和屈服强度。     

选区激光熔化24CrNiMoY合金钢组织演化与力学性能

目的 为了获取具有高抗拉强度与高伸长率的24CrNiMoY合金钢,用选区激光沉积(SLM)方法进行打印。方法 以24CrNiMoY合金钢粉末为材料,当搭接宽度为0.09 mm、扫描角度为67°、扫描线长度为10 mm、扫描速度为1 000 mm/s时,在能量密度分别为102、116、129、142 J/mm³条件下打印合金钢样品,采用金相、X射线衍射、扫描电镜、透射电镜及拉伸试验等分析手段,对制备样品的微观组织和力学性能进行研究。结果 在所采用的能量密度范围内,SLM制备24CrNiMoY合金钢的显微组织主要是板条马氏体组织,随着能量密度的增加,样品内部的气孔缺陷先减少后增加,硬度和拉伸性能以及冲击韧性呈现先升高后降低的趋势。在能量密度为116 J/mm³时,打印合金钢样品具有最优的综合力学性能,致密度为99.53%,硬度为(388±5.9)HV0.2,抗拉强度为(1 210±11) MPa,屈服强度为(1 124±10) MPa,断后伸长率为(6.2±0.4)%,冲击韧性为80 J/cm²。结论 在SLM打印24CrNIMoY合金钢样品中,较高的致密度及精细的板条马氏体是合金钢样品具有良好力学性能的关键要素,该研究可为SLM打印高抗拉强度与高伸长率的24CrNiMoY合金钢制动盘零件提供重要参考。     

电子束快速成形TC4合金的组织与断裂性能

利用超景深显微镜和扫描电镜对电子束选区熔化快速成形的沉积态TC4试样组织与断口形貌进行观察和分析,研究不同几何成形和加载方向对断裂性能的影响。结果表明,断裂性能在垂直试样中受到柱状晶组织的影响,具有各向异性,在沉积方向上的断裂韧度为94.94MPa·m^1/2,大于电子束扫描方向的断裂韧度85.33MPa·m^1/2,而伸长率很小,仅为3%;α相形态对断裂性能有影响:水平试样片层状的α集束组织伸长率及断裂韧度优于垂直试样相互交错的针状α组织,最大值为14.5%和101.45MPa·m^1/2,而抗拉强度和屈服强度较小;电子束选区熔化制备的TC4试样断口由许多不同尺寸的韧窝和弯曲的撕裂棱组成,断裂方式以延性韧窝状沿晶断裂为主,水平试样的断口撕裂棱曲折程度、韧窝尺寸和深度大于垂直试样。     

FV520B沉淀硬化不锈钢的MAG堆焊再制造力学特性

采用堆焊熔敷成形技术进行FV520B沉淀硬化不锈钢再制造实验,并通过与基材相应性能进行对比分析,研究FV520B不锈钢MAG堆焊再制造成形层力学特性。结果表明:FV520B不锈钢MAG堆焊再制造成形层具有高强度和高硬度特性,其抗拉强度达到1195MPa,超过基材的1092MPa,屈服强度和硬度平均值分别为776MPa和336HV,与基材的859MPa和353HV相近;但是,再制造成形层的静拉伸伸长率与冲击韧性相对较低,分别为8.72%和61J/cm2,与基材的19.67%和144J/cm2相比差距较大。试样断口和组织分析表明,MAG堆焊再制造成形层的快冷非平衡结晶板条马氏体+NbC,MoC,M23C6等碳化物沉淀强化相组织是其具有高强度和高硬度力学特性的根本原因。不过,缺少时效处理和Cu元素强化相作用,以及夹杂脆性相和大尺寸球形颗粒与基体间的弱界面作用会恶化材料受力时的变形能力,容易引起应力集中并开裂,是再制造成形层具有较低静拉伸伸长率和较差冲击韧性的主要原因。     

固溶处理对激光选区熔化AlSi10Mg合金显微组织、拉伸性能和残余应力的影响EICSCD

利用光学显微镜、场发射扫描电子显微镜、透射电子显微镜、拉伸实验和拉曼光谱仪研究固溶处理对激光选区熔化AlSi10Mg合金的显微组织、拉伸性能和残余应力的影响规律。结果表明:沉积态合金组织细小,强度较高,但存在明显的各向异性和较大的残余拉应力。直接人工时效后,抗拉强度和屈服强度均明显提升,但熔池和共晶硅的形貌与沉积态合金基本相同。固溶处理可以显著改善组织和拉伸性能的各向异性,彻底消除残余拉应力,但导致组织粗化,合金的抗拉强度和屈服强度仅为沉积态的50%左右。在固溶处理的基础上进行人工时效,合金的组织特征、各向异性和残余应力情况无明显变化,抗拉强度和屈服强度分别达到330 MPa和270 MPa,断后伸长率约为10%~11%。人工时效后强度的提升主要得益于GP区的析出。     

薄壁管壳体环矢挤压缩径工艺仿真分析与研究

目的 针对空心薄壁件在缩径成形工序中力学性质难以观测且缩径成形加工效率较低的问题,提出一种使用18瓣环矢挤压模具进行环矢挤压一次性成形的缩径工艺,并研究了该工艺下薄壁管壳体的弹塑性变形规律。方法 以外径6.3 mm、壁厚2 mm、颈缩宽度1 mm的小尺寸薄壁管壳体（Q255材料）为研究对象,基于Barlat’96屈服准则和M–K沟槽理论,结合L.H.Donnell理论,建立管壳体环矢挤压缩径的塑性微元应力模型,通过ANSYS软件建立环矢挤压缩径工艺有限元模型,并进行数值模拟分析,获得管壳体环矢挤压过程中内壁面和颈缩区厚度方向的应力分布规律;最后进行实验验证,利用千分尺测量外径,采用应力测定仪测量中心位点应力,验证了该工艺下仿真结果的准确性。结论 颈缩区域宽径比越大,缩径成形越远离弹性区;内壁面的应力整体呈凸状分布;卸载后,壁厚方向的残余应力呈从外壁到内壁逐渐增大的线性分布趋势,缩径区中心点最大残余等效应力为319.76MPa,分布在挤压部位的内表面;经实验验证,内壁面中心位点的最大残余应力为183MPa,其与仿真分析结果（202.5MPa）的吻合度高达91.5%,验证了仿真结果的准确性...     

CMT电弧增材制造GH4169合金的组织和拉伸性能

目的研究冷金属过渡CMT电弧增材制造GH4169合金单道多层薄壁试样的组织和拉伸性能。方法利用CMT增材制造成形系统进行GH4169合金的单壁墙增材制造试验,分析了成形薄壁试样的组织演化和力学性能,讨论了柱状晶组织的各向异性以及均匀化处理对合金力学性能的影响。结果成形试样的显微组织主要为γ相和共晶(γ+Laves)相,试样沿沉积方向具有[100]择优取向。枝晶组织随着沉积层数的增加变得粗大,枝晶间距变大且二次枝晶臂变小,Laves相的取向特征越明显。从底部区域到顶部区域,试样枝晶臂间距λ_1从13.76μm增大到23.27μm。沿柱状晶生长方向的抗拉强度最大,约为774 MPa;而沿电弧行走方向的抗拉强度随沉积层数的增加逐渐减小,断后伸长率逐渐增大,最大抗拉强度约为763MPa。1170℃固溶+时效处理后,原粗大柱状晶形成较小的多边形晶粒,成形试样组织的均匀性提高,沉积方向最大抗拉强度为1222 MPa,沿电弧行走方向最大抗拉强度为1085 MPa。结论 CMT增材制造GH4169合金组织特征与激光增材制造的试样基本一致,热处理前后CMT成形GH4169合金试样抗拉强度均小于激光立体成形,但伸长率更大。     

激光选区熔化与铸造成形TC4钛合金的力学性能分析

借助有限元模拟、光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)和维氏硬度仪研究了激光选区熔化和铸造成形TC4钛合金的微观组织演变及力学性能,进一步分析了不同成形条件下液态金属凝固冷却对其微观组织和力学性能的影响。结果表明:激光选区熔化与铸造成形的TC4钛合金分别为针状马氏体α'相的网篮组织、α+β相的魏氏组织。与铸造相比,激光选区熔化成形TC4钛合金具有极快的冷却速率(1.78×107℃·s~(-1))和较高的温度梯度,元素类型相同,晶体取向明显。同时,利用激光选区熔化(SLM)技术成形的TC4试样的抗拉强度、屈服强度、伸长率和硬度分别为1 120.83 MPa、916.31 MPa、9.5%和123.04HV,而铸造试样的抗拉强度、屈服强度、伸长率和硬度分别为917.67 MPa、786.23 MPa、8.0%和77.876HV。与铸造成形相比,SLM成形的TC4试样的抗拉强度、屈服强度、伸长率和硬度增大,分别提升了22.14%、16.54%、18.75%和58%,因此激光选区熔化成形的TC4试样具有较好的力学性能。     

激光选区熔化成形工艺对304L不锈钢冲击韧性的影响

目的 了解激光选区熔化(SLM)成形工艺参数对304L不锈钢冲击韧性的影响,从而得到304L不锈钢的最佳成形工艺参数。方法 对激光功率300~340 W,激光扫描速度800~1 500 mm.s^?1条件下的激光选区熔化成形304L不锈钢开展冲击试验,通过表面硬度、微观组织及断口形貌观察对冲击韧性的影响规律进行分析。结果 SLM成形304L不锈钢微观组织为跨越熔池生长形成的不规则柱状晶粒,成形工艺参数对试样表面硬度影响不显著;随着激光功率的增大和激光扫描速度的降低,304L不锈钢断面致密程度提高,孔洞类缺陷尺寸减少且数量减少,冲击韧性增大,冲击功最大值为141.9 J。结论 基于冲击试验结果,在激光体能量密度为100~140 J/mm³的条件下,304L冲击韧性稳定在138 J左右,为SLM成形304L材料的最佳成形参数区间。     

成形角度对选区激光熔化4Cr5MoSiV1钢组织和性能的影响EI北大核心CSCD

选区激光熔化(SLM)成形4Cr5MoSiV1钢具有良好的强/硬度以及耐磨性是提高其使用寿命的重要保证,为优化SLM成形4Cr5MoSiV1钢的组织和性能,研究不同成形角度下4Cr5MoSiV1钢试样的显微组织、显微硬度、拉伸性能和耐磨性。结果表明:随成形角度的增加,试样熔道间的热量累积程度降低,晶粒尺寸减小,细晶强化作用增强,故试样的显微硬度升高。随成形角度的增加,拉伸试样的滑移搭接面数量增多,滑移程度增加,且熔道边界处分正应力值降低,故试样的抗拉强度和断裂伸长率均升高。磨损试样的磨损机制以黏着磨损和氧化磨损为主,且随成形角度增加,试样的耐磨性升高。同一成形角度下,试样底层表面经多次热量累积后,其细晶强化和固溶强化作用减弱,显微硬度和耐磨性均降低。SLM成形4Cr5MoSiV1钢试样的显微硬度、耐磨性和拉伸性能呈正相关,45°成形角度下试样的力学性能最高,抗拉强度最高为1576.5 MPa,断裂伸长率最高为17%,顶层表面的显微硬度最高为608.4HV,顶层表面的磨损率最低为4.95×10^(-9)kg·N^(-1)·m^(-1)。     

选择性激光熔化(SLM)成形纯钨的微观组织与力学性能研究

目的 研究选择性激光熔化(SLM)技术制备的成形钨的微观组织和力学性能。方法 采用纯钨粉末作为原材料,利用SLM技术制备了高密度的纯钨试样,系统研究其孔隙与裂纹的形成机理。同时,利用光学显微镜、显微维氏硬度计和压缩实验等分析手段,分别沿水平面(x-y)和垂直平面(z-x)对其微观组织与力学性能进行分析,探究SLM成形纯钨的各向异性。结果 成功制备了相对密度为97.79%的高致密纯钨试样,在水平面上,组织主要为呈长条形的柱状晶,在垂直平面上,组织为粗大的胞状晶,断口形貌表现为典型的宏观脆性断裂特征。在水平面上,试样具有更高的抗压强度(1 100 MPa)和显微硬度(427±5)HV。结论 孔隙的形成主要与Marangoni效应有关,而裂纹的产生主要取决于材料本身的特性和SLM工艺参数。组织的各向异性导致2个平面的力学性能有一定差异。     

Latent hardening in polycrystalline copper and comparison with high density polyethylene

When a parallelepiped specimen of polycrystalline copper is compressed in thex-direction (primary direction) while holding thez-dimension unchanged by a vice, the specimen is anisotropically hardened as follows: when thez-direction is subsequently compressed while holding thex-dimension unchanged the yield stress (0.2% offset) is higher than the final flow stress of the primary deformation. This is similar to latent hardening in single crystals. On the other hand, if the second compression is in they-direction instead of thez-direction, the yielding (0.2% offset) occurs at a stress less than the final flow stress of the primary deformation. Both effects are reported here together with the results of two successive compressions in two mutually perpendicular directions without any constraints in either compression. These results are compared with the earlier results of high density polyethylene.     

Preparation and properties of nano-SiC strengthening Al2O3 composite ceramics

The processing and mechanical behaviors of Al₂O₃-xwt.%SiC (x = 1, 2, 5, ASx) nano-composites prepared by the in situ synthesis of SiC from polycarbosilane (PCS) were investigated. The composites were densified by hot pressing. The microstructure and mechanical properties of the sintered composites were analyzed. The results showed that a fully dense structure was obtained when a few nano-SiC were doped and that the fracture toughness and strength were highly improved compared with those of monolithic Al₂O₃. The fracture toughness reached 5.1 MPa m^1/2 in AS2 composite. The maximum flexural strength was 516 MPa obtained in AS1 composite.     

SiCf/O′-SiAlON composite: properties and oxidation retained properties

A composite of O′SiAlON (Si_2-xAl_xN_2-xO_1+x, with x 0.14) reinforced with 20 vol.% SiC monofilaments was fabricated by hot-pressing, at 1600°C, for 2 h under 34 MPa pressure. The mechanical and interfacial properties of the composites, as-fabricated as well as post-oxidized, were, investigated. The composite exhibited a significant improvement in ultimate flexure strength (640 MPa) and work of fracture (42 kJ m⁻²) compared with that (350 MPa and 1.8 kJ m⁻², respectively) of the monolithic material. These mechanical properties were slightly increased after the composite was heat treated for 24 h in air at 1200 and 1300°C. However, the composite exhibited a significant degradation in ultimate strength, while the work of fracture (WOF) remained unchanged after exposure in air at temperatures beyond 1400°C. The as-fabricated composite revealed a low interfacial shear strength (6.2 MPa) and a frictional sliding stress (3.2 MPa). After the composite was oxidized at elevated temperatures, the interfacial bonding and sliding stresses were reduced to noticeable extents, resulting from the degradation of the carbon coating layer of the SiC monofilaments.     

Al2O3-ZrO2复相陶瓷压缩变形织构及其对组织性能的影响

采用真空热压烧结法制备了3Y-ZrO2/Al2O3细晶复相陶瓷,对其致密块料进行了高温压缩变形,分析了材料变形前后的显微组织和力学性能.结果显示,XRD及X射线极图显示压缩变形后的陶瓷材料具有明显的织构特征,最大织构强度达到7.3.织构化陶瓷的弯曲强度,断裂韧性和维氏硬度值随应变量的增加呈逐步增大的趋势,最大值分别为933.8MPa,10.4MPa·m1/2和20.4GPa.当真应变很高(1.72)时,力学性能呈现一定幅度的降低趋势.分析表明织构化可以大幅提高材料的力学性能,同时极高变形量下形成的粗化晶粒和大尺寸空洞又导致力学性能的降低.     

Systematic investigation of acicular ferrite formation on laboratory scale

By increasing the amount of acicular ferrite (AF) in the microstructure, steel toughness can be improved significantly. The steel composition, cooling rate, non-metallic inclusions and austenite grain size have a strong influence on the formation of AF. The present paper describes and compares two approaches to study AF formation in a titanium-deoxidised high-strength low-alloyed steel and its influencing factors on laboratory scale: route A simulates the formation of AF after heat treatment; route B simulates the formation directly after solidification of the melt. The formation of AF is essentially influenced by the former processing, which also changes the optimum cooling parameters substantially. (Ti,Mn)_xO_y and (Ti,Al,Mn)_xO_yS_z are the predominant active inclusion types in the investigated steel.     

A study of the stabilization of aluminium titanate

A tialite ceramics (Al₂TiO₅) was synthesized at a temperature of 1500 °C, incorporating CaF₂, La₂O₃, SiO₂ or kaolin and MgO additives. Its thermal stability was investigated by thermocycling in a reducing medium. The batches containing SiO₂ or kaolin additives underwent a decomposition to rutile and corundum. A stabilized ceramic with added MgO was produced. X-ray and electron-probe microanalysis established the presence of Mg/Al, Ti_z/O₄, Al_2–x-y Ti_1+x Mg _y O₅ and Ca_1–x La _x /Al_12–y-z Mg _y Ti _z /O₁₉ solid solutions, which retained their chemical composition after thermocycling in a reducing medium.     

Effects of T-stresses on fracture initiation for a closed crack in compression with frictional crack faces

This paper studies crack extension resulting from a closed crack in compression. The crack-tip field of such a crack contains a singular field relative to K _II and non-singular T-stresses T _x and T _y parallel and perpendicular to the crack plane, respectively. Using a modified maximum tensile stress criterion with the singular and non-singular terms, the kinking angle at the onset of crack growth is determined by a two parameter field involving the mode-II stress intensity factors and T-stresses, and at fracture initiation a wing crack may be created at an arbitrary angle from 0° to 90°. A compressive T _y increases the kinking angle and reinforces apparent mode-II fracture toughness, while a compressive T _x decreases the kinking angle and enhances apparent mode-II fracture toughness. The direction and resistance of fracture onset is strongly affected by T-stresses as well as frictional stress. The von Mises effective stress is determined for small-scale yielding near the crack tip. The effective stress contour shape exhibits a marked asymmetrical behavior unless 2T _x  = T _y  ≤ 0 for plane stress state. Coulomb friction between two crack faces generally increases the kinking angle, shrinks the size enclosed by the effective stress contour and enhances apparent fracture toughness. Field evidence and experimental observations of many phenomena involving the growth of closed cracks in compression agree well with theoretical predictions of the present model.     

GaxIn1 ? xBiyAszSb1 ? y ? z/InSb and InBiyAszSb1 ? y ? z/InSb heterostructures grown in a temperature gradient

Heterophase equilibria in the Ga _x In_{1 − x} Bi _y As _z Sb_{1 − y − z} -InSb and InBi _y As _z Sb_{1 − y − z} -InSb systems have been analyzed within the simple solution approximation. Ga _x In_{1 − x} Bi _y As _z Sb_{1 − y − z} /InSb and InBi _y As _z Sb_{1 − y − z} /InSb heterostructures have been grown in a temperature gradient, and their composition and structural perfection have been assessed.     

C合金化对AlCrFeCoNi2.1共晶高熵合金微观组织和拉伸性能的影响

目的 为了显著提高AlCrFeCoNi2.1共晶高熵合金的室温力学性能,利用C合金化的方法研究不同碳含量对微观组织和室温拉伸性能的作用规律。方法 采用电弧熔炼–滴铸方法制备了不同C含量的(AlCrFeCoNi2.1)–x%C(x=0、1、2、3,原子数分数)共晶高熵合金,利用XRD、SEM和EDS等手段研究了不同C含量下微观组织、相结构和拉伸性能的变化规律。结果 添加C元素后,合金未形成新相,仍然由FCC相和B2相组成,但其微观组织呈现出由层片状向树枝晶转变的特征。随着C含量的增加,屈服强度和抗拉强度增大,但伸长率有一定的降低,其中(AlCrFeCoNi2.1)–3%C(原子数分数)合金的屈服强度可达到791 MPa,抗拉强度可达到1 332 MPa,同时伸长率仍有6.1%,与AlCrFeCoNi2.1合金相比,屈服强度和抗拉强度分别提高了99 MPa和296 MPa。结论 该强化效果主要来源于C原子的固溶强化作用和微观结构的改变。