不同铸型对TC4钛合金的微观组织、织构和持久性的影响

研究不同铸型成型下TC4钛合金的微观组织、织构和高温持久性能,利用光学显微镜(OM)、X射线衍射(XRD)、扫描电子显微镜(SEM)和电子背散射衍射(EBSD)等观察和分析TC4钛合金的显微组织与持久性断裂行为。结果表明：不同铸型工艺TC4钛合金的物相均为α相、β相和ω相组成,其中主要物相为α相(90%左右)。与石墨型相比,陶瓷型有利于β→α相变,α相高出5.3%,晶粒平均直径大(d_mean=37.021μm),晶界较少,晶粒均匀相对稳定,当α相比例增大时,材料强度减小,塑性升高。同时陶瓷型织构强度高,取向明显,织构类型为{11-20}<1-100>,与Y方向呈现约45°的夹角,进一步验证了试样在(101)、(002)、(101)峰强增加的原因,与织构的形成有关;陶瓷型试样的高温持久性优于石墨型,在温度(400℃、430℃、460℃)下,持久性应力断裂寿命分别提高了1.174%、15.401、6.998%,均为韧性断裂,其微观形貌为韧窝花样。此外,温度直接影响TC4钛合金的持久寿命,随着温度升高,TC4钛合金的应力断裂寿命逐渐降低。     

冷却方式对TC16钛合金丝材组织与力学性能的影响

首先分别对在单相区(880℃)和两相区(840℃)加热保温2 h后的TC16钛合金丝材进行3种不同方式的冷却处理(水冷、空冷、炉冷),随后采用光学显微镜、扫描电镜、X射线衍射、拉伸性能测试以及冲击性能测试等研究了该合金经不同方式冷却处理后的组织和力学性能。结果表明：当加热温度位于两相区时(840℃),合金的组织由等轴α相构成,当加热温度位于单相区时(880℃),组织中等轴α相完全消失,并出现β晶粒。3种冷却方式中,经空冷处理后,合金的强度最高,水冷次之,炉冷最低,而冲击性能与强度相反,在塑性方面,经水冷处理后,合金的塑性最佳,炉冷次之,空冷最差。合金在两相区加热保温2 h后以不同方式冷却处理后,拉伸和冲击断口微观形貌均以韧窝和解理面为主,其中炉冷试样的冲击断口形貌中具有较多二次裂纹,经单相区加热后,空冷试样的拉伸和冲击断口形貌产生较大变化,出现结晶状和河流状形貌。     

一种新型低成本阻燃钛合金的微观组织与力学性能

研究了一种名义成分为Ti-25V-15Cr-5Mo-0.25Si-0.08C的新型低成本阻燃钛合金TF-X,通过三次真空自耗熔炼制备了φ120mm铸锭,经包套挤压得到φ25mm棒材,观察了铸锭和挤压棒材的微观组织,测试并分析了挤压棒材的室温和高温拉伸性能、热稳定性能、高温蠕变性能。结果表明：TF-X合金具有与TF550合金大致相同的微观组织;TF-X合金室温及高温拉伸强度高于TF550合金,并且具有很好的塑性;试验条件下,TF-X合金的热稳定性能低于TF550合金,熔炼过程中应该严格控制氧含量;TF-X合金在540℃/250MPa/100h条件下蠕变性能与TF550合金相当,显著高于Ti40合金。     

变形量对Ti-55531钛合金微观组织和力学性能的影响

为了进一步优化Ti-55531钛合金的锻造过程,分析了变形量对其微观组织和力学性能的影响。通过不同变形量下的镦粗实验,分析了Ti-55531钛合金锻后的微观组织,并对锻后样品进行了β退火+时效热处理,最后进行了拉伸测试。结果表明,随着变形量的增加,Ti-55531钛合金中初生α相的体积分数逐渐下降,热处理后初生α相消失,微观组织以次生α相为主。Ti-55531钛合金的平均强度随着变形量的增加逐渐下降,而其塑性随着变形量的增加逐渐增加,结合企业生产标准,同时为了避免各向异性,应将变形量范围控制在30%～50%。     

冷轧对CT20钛合金微观组织和力学性能的影响

选取通过轧制工艺制备的四种不同厚度的CT20钛合金板材,采用多种技术对其微观组织进行表征,测试板材的硬度以及沿轧件的轧制方向(RD)和横向方向(TD)拉伸的力学性能,分析微观组织与力学性能之间的内在联系。结果表明：在冷轧过程中,高密度的位错触发了合金的非晶化转变,变形量的增大使α相沿RD伸长,β相和β_t组织破碎。位错和亚结构数量的提高不仅使合金硬度上升,而且使RD和TD的拉伸强度增大,伸长率下降。RD的断裂类型属于韧性断裂,TD的断裂类型属于韧脆混合型断裂。在冷轧过程中,基面滑移和柱面滑移共同参与织构的演变,由此形成的织构取向对板材RD和TD两方向的滑移行为和力学性能产生了重要影响;同时,由于位错在RD和TD两方向上的滑移距离不同导致不同的加工硬化阶段。     

热处理对TA19钛合金组织和力学性能的影响

通过改变固溶温度、固溶后的冷却方式和时效温度,研究了热处理制度对TA19钛合金微观组织和力学性能的影响。研究表明,随着固溶温度的升高,初生α相含量减少,使得伸长率和断面收缩率减小;而升高固溶温度使得β相中析出的细小次生α相增多,从而使室温抗拉强度增大。固溶处理后采用水冷时,由于从β相中析出大量细小弥散的次生α相,室温抗拉强度较大,但伸长率和断面收缩率较小。时效温度对微观组织和力学性能影响较小。     

时效温度对Ti-5Al-4Zr-10Mo-3Cr钛合金微观组织及力学性能的影响

研究了Ti-5Al-4Zr-10Mo-3Cr合金经过β相区固溶(880 ℃)、不同温度时效(540~620 ℃)处理后次生α相(α_s)析出形貌及其对力学性能的影响。结果表明:随着时效温度由540 ℃升高至620 ℃,合金中析出α_s相片层厚度由0.030 μm增加到0.142 μm,屈服强度由1353 MPa降低至1074 MPa,断后伸长率由2.5%升高至11.4%,即时效析出的微米级片层α_s能够显著调控合金的力学性能。此外,时效温度升高使合金的拉伸断裂由沿晶脆性断裂为主转变为韧窝穿晶为主的韧性断裂方式。Ti-5Al-4Zr-10Mo-3Cr合金时效析出的片层状α_s相的厚度大于0.1 μm,合金的断后伸长率≥6%。当时效温度为600 ℃时,合金的硬度为387 HV10,抗拉强度为1182 MPa,伸长率为8.5%,具有良好的强塑性匹配。     

热处理工艺对TC11钛合金组织及性能的影响

研究了热处理温度和冷却方式对初始组织为等轴组织的TC11钛合金显微组织及力学性能的影响.结果表明,对于TC11钛合金,在空冷条件下,随热处理温度的升高,等轴α相含量逐渐减少;当热处理温度超过980 ℃,合金开始发生组织形态的改变,由初始的等轴态转变为α β双态组织,随温度的继续升高,等轴组织完全转变成片层状组织;热处理温度在980 ℃以上时,随冷却速度的增加,β转变组织的片层厚度逐渐减小,冷却速度较快时(水冷),形成淬火马氏体.拉伸试验研究表明,热处理温度为980～1020 ℃,空冷(或油冷)条件下,得到的组织具有较好的高温综合力学性能,其中热处理温度在980～1000 ℃之间得到的组织由于等轴α相含量约为50%,具有最佳的力学性能.     

变形条件对钛合金微观组织的影响

以钛合金为研究对象,利用Gleeble-3500热模拟试验机进行热模拟试验,分析不同变形条件对钛合金微观组织的影响。该研究为探索低成本钛合金的微观组织提供理论依据和实验依据。     

变形条件对钛合金微观组织的影响

以钛合金为研究对象,利用Gleeble-3500热模拟试验机进行热模拟试验,分析不同变形条件对钛合金微观组织的影响。该研究为探索低成本钛合金的微观组织提供理论依据和实验依据。     

凝固速度和时效处理对高强高导Cu-3.2Ni-0.7Si合金组织与性能的影响*

通过单辊旋淬快速凝固技术制备Cu-3.2Ni-0.7Si（wt%）合金薄带。研究了不同旋淬速度（凝固速度）和时效处理对合金微观组织、导电率和力学性能的影响。结果表明,随着凝固速度的增大,铸态合金的晶粒明显细化,导电率降低,显微硬度和拉伸强度升高。铸态合金在同一温度进行时效处理,随着时效时间的增加,合金的电导率呈升高趋势,而合金的显微硬度和拉伸强度先升高后降低。铸态合金的导电率随凝固速度的增大而降低是基体晶格畸变程度增大所致;合金时效处理后导电率升高是由于第二相析出明显消除晶格畸变的结果。铸态合金显微硬度和拉伸强度随凝固速度增大而升高是细晶强化的结果;时效处理后,合金的显微硬度和抗拉强度明显提高是第二相强化的结果,而过度时效导致显微硬度和拉伸强度降低的主要原因是第二相的粗化团聚所致。     

SiC含量对近β钛合金显微组织及力学性能的影响

通过真空非自耗熔炼工艺制备了不同SiCp添加量(0wt.%、0.1wt.%、0.4wt.%、1.wt.%)的近β钛合金。采用X射线衍射仪(XRD)、扫描电镜(SEM)、维氏显微硬度计和万能材料试验机,系统研究了SiCp添加量对近β钛合金显微组织及力学性能的影响规律。研究结果表明,不同SiCp添加量的近β钛合金主要由α-Ti、β-Ti和TiC所组成。近β钛合金的初生β晶粒尺寸取决于SiCp的添加量,SiCp添加量由0%增加到1wt.%时,近β钛合金初生β晶粒尺寸由639μm降低至323μm。由于受细晶强化、TiC承载强化以及Si的固溶强化的影响,随着SiCp添加量的增加,近β钛合金的显微硬度、压缩强度有显著提高,而压缩率却明显降低。     

Cooling Rate Sensitivity of RE-Containing Grain Refiner and Its Impact on the Microstructure and Mechanical Properties of A356 Alloy

The cooling rate sensitivities of Al Ti B, RE and Al Ti B–RE refiners were investigated using laboratory experiments and the actual industrial applications of A356 automotive wheel via low pressure die casting technology. Their impact mechanisms on the microstructure and mechanical properties of the A356 alloy were discussed. The results demonstrated that the Al Ti B–RE refiner possessed most effective and synergetic refinement effects compared to the individual Al Ti B or RE refiners. The Al Ti B–RE refiner exhibited the least sensitivity to the cooling rate changes than the other refiners. The comprehensive properties of alloy wheel refined by the Al Ti B–RE refiner were improved significantly.The tensile strength, yield strength, and elongation of wheel spoke improved by approximately 11.3%, 10.8% and 44.1%,respectively. The property difference values of the tensile strength, yield strength, and elongation in different positions of the wheel decreased from 14.8%, 31.2% and 47.7% to 8.6%, 27.1% and 30.9%, respectively.     

热变形对TC11-Ti2AlNb电子束焊接件力学性能的影响

本文应用纳米压痕和维氏硬度的方法表征了TC11/Ti2AlNb电子束焊接焊缝区域在不同状态下的硬度和弹性模量分布,结合组织的演变分析了微纳米尺度的力学的变化。结果表明：在TC11合金的热影响区,马氏体α&quot;相的分解是显微硬度降低的主要原因;而在焊缝以及Ti2AlNb热影响区区域,相的析出导致了显微硬度的增加。通过热变形以及锻后热处理都能够提高焊接区域的弹性模量。相比较而言,焊接态的焊缝弹性模量只有92GPa;而在变形和热处理后,弹性模量的值达到了130GPa。通过拉伸实验结果分析,焊缝在变形及热处理后屈服强度得到了较大提高,这和焊缝区域硬度和弹性模量的变化趋势一致。     

Fatigue Failure of Ductile Iron Crankshafts

Abstract

Automobile crankshafts can be produced as either steel forgings or ductile-iron castings. In the latter case, because of the high structure-sensitivity of fatigue strength, mechanical test requirements must be very specific. A detailed investigation of two series of crankshafts produced from pearlitic nodular-graphite iron, grade SG 60, is described. Normal tensile tests and microstructural examinations were supplemented by determination of fatigue life and fatigue limit. Fatigue tests under axial bending conditions were carried out on segments taken from two series (I, II) of machined crankshaft castings. Satisfactory bending moment and performance data were obtained for one series of samples. In the other series, sub-surface microporosity in the cast structure was exposed during subsequent machining and led to premature fatigue failure after less than 2 × 10⁵ cycles of testing.     

钛对ZL108合金组织和力学性能的影响

本文试验研究了钦对ZL108合金组织和强度、塑性、硬度、冲击韧性的影响,进行了定量金相及断口、亚表层组织分析。结果表明:含钛的ZL108合金组织中存在针片状Al_3Ti化合物;对该合金有强化和脆化作用;亦有高温强化作用。对于活塞合金,应改善含钦ZL108合金的室温塑韧性及更进一步地开发其高温强化效果。     

Steel to titanium solid state joining displaying superior mechanical properties

Joint configuration with Ti inserts, which allows the increase of the bonded area of similar materials at the expense of that of dissimilar ones, is suggested. The force to failure for the specimens with the suggested configuration was about two fold higher than that for the specimens with the planar interface. Microstructural analysis of the joints, fracture characterization, mechanical testing and finite elements simulation were conducted in order to elucidate the mechanical behavior of the suggested joint configuration. Failure of joints with Ti-inserts is governed by the brittle behavior of TiC and α-Ti layers, located at the steel–Ti interface, with cracks initiation within the interfacial layer. The cracks propagate first into the brittle α-Ti phase and then cause the fracture in the Ti/Ti bond. The results of finite elements analysis are in good agreement with the analysis of the fracture surfaces.     

Ti—Al二元合金的成分对组织和力学性能的影响

用金相、扫描电镜和X射线衍射研究了6种不同Al含量Ti-Al二元合金铸态和退火态的组织结构和相组成的特征和变化。从结晶动力学的观点,分析了合金的结晶凝固过程。采用三点弯曲方法研究了合金的抗弯性能同Al含量的关系。结果表明,Al含量为34 wt%,经1100℃/30 h退火的合金抗弯性能最好,Al含量偏离34wt%,都对合金的力学性能不利。     

Characterization and comparison of materials produced by Electron Beam Melting (EBM) of two different Ti–6Al–4V powder fractions

Electron Beam Melting (EBM) has been recognized as a revolutionary technique to produce mass-customized parts to near-net-shape from various metallic materials. The technique produces parts with unique geometries from a powder stock material and uses an electron beam to melt the powder layer-by-layer to fully solid structures. In this study we have investigated the use of two different Ti–6Al–4V powders of different size fractions in the EBM process; a larger 45–100 μm powder, and a smaller 25–45 μm powder. We have also investigated the effects of two build layer thicknesses, 70 μm and 50 μm, respectively. We hypothesize that the smaller powder has the potential to improve surface resolution of parts produced in the EBM process. The EBM as-built parts were investigated regarding surface and bulk chemistry, surface oxide thickness, macro- and microstructure, surface appearance and mechanical properties. We conclude from the results that both powders and both build layer thicknesses are feasible to use in the EBM process. The investigated material properties were not significantly affected by powder size or layer thickness within the studied range of process parameters. However, the surface appearance was found to be different for the samples made with the different powder sizes.