Simulations and Experiments of the Nonisothermal Forging Process of a Ti-6Al-4V Impeller

In the present study, a nonisothermal precision forging process of a Ti-6Al-4V first-stage impeller for the gas turbine engine was simulated using the finite element software. The simulation results such as load requirements, damage, velocity field, stress, strain, and temperature distributions are discussed in detail. Simulations predicted the maximum load requirement of about 80 MN. The maximum temperature loss was observed at the contour surface regions. The center and contour regions are the high-strained regions in the part. To validate the model, forging experiments mimicking simulations were performed in the α + β phases region (930 °C). The selected locations of the part were characterized for tensile properties at 27 and 200 °C, hardness, microstructure, grain size, and the amount of primary α phase based on the strain distribution results. The soundness of the forged part was verified using fluorescent penetrant test (Mil Std 2175 Grade A) and ultrasonic test (AMS 2630 class A1). From the experimental results, it was found that the variations in the hardness, tensile properties at room, and elevated temperature are not significant. The microstructure, grain size, and primary α phase content are nearly same.     

等温锻造温度对2A70铝合金组织性能的影响

在6300kN四柱油压机上对2A70铝合金试样在变形温度350～480℃、应变速率0.001s~(-1)的条件下进行等温压缩试验,然后对其进行标准同溶时效处理,并进行室温拉伸性能测试和显微组织观测.实验研究结果表明,在430～450℃变形温度范围内,等温锻件的显微组织为完全再结晶组织,晶粒细小且沿变形方向分布;在430℃纵向抗拉强度和屈服强度分别达到最大值(410MPa和292.5MPa),在450℃横向抗拉强度和屈服强度分别达到最大值(400MPa和270MPa),而伸长率均远超过技术条件要求.综合考虑显微组织、强度和塑性等因素,选取450℃为该合金的较佳等温锻造温度.     

Microstructure Modeling of a Ni-Fe-Based Superalloy During the Rotary Forging Process

The microstructure evolution of Ni-Fe superalloys has a great influence on the mechanical behavior during service conditions. The rotary forging process offers an alternative to conventional bulk forming processes where the parts can be rotary forged with a fraction of the force commonly needed by conventional forging techniques. In this investigation, a numerical modeling of microstructure evolution for design and optimization of the hot forging operations has been used to manufacture a heat-resistant nickel-based superalloy. An Avrami model was implemented into finite element commercial platform DEFORM 3D to evaluate the average grain size and recrystallization during the rotary forging process. The simulations were carried out considering three initial temperatures, 980, 1000, and 1050 °C, to obtain the microstructure behavior after rotary forging. The final average grain size of one case was validated by comparing with results of previous experimental work of disk forging operation. This investigation was aimed to explore the influence of the rotary forging process on microstructure evolution in order to obtain a homogenous and refined grain size in the final component.     

GH4169合金涡轮盘热模锻中晶粒尺寸演变的数值模拟与分析

针对GH4169合金涡轮盘热模锻中易出现粗晶、混晶等显微组织缺陷,通过热模拟压缩实验和热变形后热处理实验,研究分析了GH4169合金在热变形和后续热处理中的显微组织演变规律,并建立了晶粒尺寸演变模型。实验结果表明:GH4169合金在热变形中的主要显微组织演变机制为动态再结晶,热变形后热处理中的主要显微组织演变机制为晶粒长大和孪晶生成。将晶粒尺寸演变模型与有限元结合,对某GH4169合金涡轮盘热模锻中的晶粒尺寸演变进行了预测分析,预测结果与实际结果一致。     

Microstructure and properties of Al<Subscript>3</Subscript>Zr/2024Al in situ composites after forging

To research the influencing rule of severe plastic deformation on Al matrix in situ composites, 10 wt% Al₃Zr/2024Al in situ particle-reinforced composite was prepared by direct melt reaction (DMR), and then, the composite was hot-forged by one direction with 90 % plastic deformation. Then, the microstructure of the forging state composite was observed, and the change law of mechanical properties and friction performances after and before plastic deforming was compared. The results indicate that the Al₃Zr-reinforced particle rotates and breaks into smaller size of 10–20 µm with the matrix flow; in addition, these smaller particles distribute more orderly in orientation and dispersedly. The 2024 matrix grain changes from as-cast tissue to fibrous tissue with length of 100 µm along the forging direction. Some mechanical properties of composites hot-forged by one direction with 90 % plastic deformation are improved much obviously. For example, the tensile strength is improved by 39.75 %, reaching 225 MPa, and the hardness is improved by 35.84 %, reaching HBW 76.83. Besides, the wear rate reduces, wear depth and area decline, and the wear-resisting property is improved after hot forging.     

Modified Law of Mixture to Describe the Tensile Deformation Behavior of Thermomechanically Processed Dual-Phase Steel

Low alloy steel containing 0.09 wt.% C was thermomechanically processed with various rolling reductions at intercritical temperature of 790 °C, followed by quenching in the iced brine solution. The flow of the material due to this plastic deformation increased the aspect ratio of the microstructure (α + γ) in the rolling than in the transverse directions. The strengths, both in the longitudinal and transverse directions of rolling were increased because of the development of substructure in ferrite, observed previously. The fibrous microstructure formed after rolling increased the surface area of contact of ferrite and martensite. During tensile deformation the fibrous dual-phase composite had positioned itself for better stress transfer from soft ferrite to hard martensite particles. These microstructural changes associated with hot deformation of the material were accommodated in current modifications in the law of mixture applied to dual-phase steel. A computer simulation was developed to present the deformation behavior of ferrite, martensite, and composite from the experimental tensile data (loads and strain). Different variables were introduced in the simulation for allowing the composite curves to pass through the experimental data points to demonstrate the tensile deformation behavior of ferrite and martensite. The systematic changes in these variables with degree of hot rolling in the intercritical region clearly described the deformation behaviour of ferrite and martensite individually.     

锻造工艺对Ti-6.5Al-1Mo-1V-2Zr合金大规格棒材的组织与性能的影响

研究三种锻造工艺条件下 Ti?6.5Al?1Mo?1V?2Zr 合金大规格棒材的力学性能、微观组织和拉伸断口。结果表明：采用拔长方式在β区高温和低温分别进行开坯锻造和成品锻造,获得的棒材的组织为粗大的魏氏组织,力学性能特别是塑性差,室温拉伸断口为脆性断口;采用镦拔方式在β区高温进行开坯锻造,再采用拔长方式在α+β区进行成品锻造,获得棒材的组织为双态组织,具有最佳的综合力学性能,室温拉伸断口为塑性断口。要获得合格的 Ti?6.5Al?1Mo?1V?2Zr 棒材,关键是开在坯锻造阶段进行充分镦拔以破碎铸锭原始组织,并在成品锻造阶段控制锻造温度和变形量。     

退火温度对EB熔炼低成本TC4钛合金宽厚板组织和性能的影响

采用EB炉一次熔炼TC4合金扁锭作为直轧坯料,在4200 mm宽厚板轧机上成功制备出规格46 mm×2650 mm×8700 mm的低成本TC4合金宽厚板,研究了退火温度对低成本TC4合金板材显微组织和力学性能的影响。结果表明:EB熔炼TC4合金扁锭经过两火换向轧制,粗大铸态组织得到充分破碎,热轧态TC4合金板材显微组织中等轴α或条状α含量较高,横纵向室温拉伸性能差异小,横向室温冲击吸收能量小于纵向,横纵向心部强度均高于表层。TC4合金板材经750~900 ℃退火,横纵截面为等轴组织,经950 ℃退火,横纵截面为双态组织,经980 ℃退火,横截面为双态组织,纵截面为魏氏组织。随着退火温度升高,TC4合金板材抗拉强度和规定塑性延伸强度呈下降趋势,伸长率基本不变,室温冲击吸收能量先升高后降低,900 ℃退火后,强度、伸长率和冲击吸收能量达到最佳匹配。     

加热温度对34MnB5热成形钢组织性能的影响

以经酸连轧后的34MnB5钢为原料,采用Gleeble3500热模拟试验机模拟退火试验,分析最佳退火温度,并进行不同热冲压工艺的平模淬火试验。研究退火温度、淬火温度对热成形钢组织与性能的影响。结果表明,退火温度为790℃时,条带状组织已基本消失,晶粒的等轴化程度较高,混晶现象明显改善,贝氏体晶粒组织细化,在基体内部均匀分布铁贝两相。退火温度为790℃,淬火温度为930℃,保温5 min时,显微组织为细小均匀的板条马氏体,综合力学性能最好,其屈服强度达到1353 MPa,抗拉强度达到2018 MPa,伸长率达到7.5%,且横纵向三点弯曲角均可以达到50°以上。     

铸态2219铝合金热压缩变形组织演变规律

为解决2219铝合金微观组织粗大、第二相分布不均的问题,开展了对铸态2219铝合金热压缩变形组织演变规律的研究。研究结果表明,经热压缩变形后,铸态2219铝合金组织中粗大的晶粒及连续网状分布的残余结晶相被打碎,经热处理后形成了均匀的再结晶组织。随着变形温度的升高,晶粒组织粗化,但Al2Cu相的分布更细小、均匀;随着变形量的增大,晶粒组织逐渐细化,晶粒大小分布也更均匀,且Al2Cu相也随变形量的增加破碎得更充分,分布更细小、均匀。在大直径铸锭锻造开坯过程中,为了获得Al2Cu相细化分布的组织,变形温度应控制在420℃以上,单次变形量不应低于50%。延长锻后保温时间不会显著影响材料的显微组织,因此,在锻造开坯过程中,为了保证合理的变形温度区间,可以采用回炉加热多火次锻造的方式。     

半固态锻造Ti14合金的拉伸性能和组织演变特征(英文)

通过室温和高温拉伸性能测试,对比研究了Ti14合金经常规锻造(950℃)和半固态锻造(1000℃和1050℃)后试样在不同温度区间的宏观力学行为,分析了微观组织演变规律、断口微观形貌及断裂特征。结果表明:合金经半固态锻造后表现出高强度、低塑性的力学特征,随着半固态锻造温度的升高,合金力学性能下降。半固态锻造过程中组织的变化是引起力学性能差异的主要原因,而组织演变的主要特征是Ti2Cu析出相形态和分布的变化。随着半固态温度的升高,更多的液相在晶界析出,并在凝固过程中析出大量板条状Ti2Cu相,最终在晶界上形成偏析带组织。这种带状组织在拉伸过程中引发了解离断裂,导致了低塑性。此外,通过再结晶退火可以有效地细化半固态组织,改善强度性能。     

Effects of Different Forging Processes on Microstructure Evolution for 316LN Austenitic Stainless Steel

Forging experiments were designed and carried out on a 3150 kN hydraulic press to investigate the effects of different processes on the microstructure evolution for 316LN steel. The forging processes included single-pass (upsetting) and multipass (stretching) deformations, and the experimental results indicated that the average grain size varied with forging processes. Moreover, the size had distinct differences at different positions in the workpiece. Meanwhile, numerical simulations were implemented to study the influence of temperature, strain, and strain rate on microstructure evolution. The results of experiments and simulations comprehensively demonstrated that dynamic, static, and meta-dynamic recrystallization could coexist in the hot forging process and that the recrystallization process could easily occur under the conditions of higher temperature, larger strain, and higher strain rate. Moreover, the temperature had more significant influence on both recrystallization and grain growth. A higher temperature could not only promote the recrystallization but also speed up the grain growth. Therefore, a lower temperature is beneficial to obtain refinement grains on the premise that the recrystallization can occur completely.     

The microstructure and properties of ultra-fine grained Ti-17 powder compact improved through isothermal forging

The microstructure and properties of hot isostatic pressed (HIP-ed) Ti-17 powder compact were improved through isothermal forging with preferable deformation parameters provided by processing map. The processing map was established based on isothermal compression experiments which were conducted at temperatures from 810 °C to 920 °C and strain rates from 0.001 s^?1 to 1 s^?1. The established processing map ascertained the value of the efficiency of power dissipation, the flow stability region and the flow instability region at different deformation conditions. Based on processing map, the isothermal forging was conducted above and below beta transus temperature to fully densify the powder compact and simultaneously improve the microstructure. After isothermal forging in flow stability regions with preferable deformation parameters, the primary coarse grains of HIP-ed Ti-17 powder compact were thoroughly broken. Many ultra-fine dynamic recrystallized grains formed and uniformly distributed in beta matrix. Both experiment data and fracture morphology of tensile sample proved that the microstructure and properties of HIP-ed Ti-17 powder compact were largely improved during isothermal forging. Final properties of prepared ultra-fine grained Ti-17 powder compact even exceeded conventional casting and forging Ti-17 alloy.     

TiAl基合金的复合热机械处理

研究了热加工和热处理对ＴｉＡｌ基合金显微组织的影响。试验发现，三向压应力能显著地提高合金的热变形塑性，实现无破损大应变速率热变形。分析表明，常规热变形工艺下试样中仍存在粗大层片状晶团，且不能由随后热处理消除，而复合热机械处理新工艺能在整个试样上得到细小、均匀的显微组织。     

超细晶钢微观组织与力学性能的各向异性研究

通过温轧技术,成功制备了平均晶粒尺寸约1μm的超细晶钢。利用扫描电镜、电子背散射衍射和室温拉伸等检测手段,研究了超细晶钢板的微观组织与力学性能的各向异性。结果表明：制备的超细晶钢板不同方向的微观组织和力学性能具有明显的各向异性;纵截面表层和心部的晶粒大多呈现拉长的形态,同时表层的晶粒拟合椭圆长/短轴比相较于心部更小,形状更加接近于圆形,横截面的晶粒拉长状特征相较于纵截面减弱,更接近等轴态,晶粒在三维空间呈细长的扁梭形态;各向强度由高到低依次为轧向、横向、与轧向成45°方向;长梭形晶粒组成的微观组织形态和织构是导致超细晶钢板力学性能各向异性明显的主要原因。     

高温短时固溶处理对超高强Al-Zn-Mg-Cu合金锻件组织与性能的影响

采用光学显微镜、扫描电镜和拉伸试验机研究了高温短时固溶处理温度(475~480 ℃)与时间(0~7 min)对高合金化Al-Zn-Mg-Cu合金锻件组织与性能的影响。结果表明,高温短时固溶处理可有效提高时效态Al-Zn-Mg-Cu合金锻件的抗拉强度及断后伸长率。随着温度或时间的增加,晶界粗大残留第二相逐渐回溶至铝基体,当温度过高或时间过长时,等轴状晶粒发生粗化,组织发生过烧现象。经对比分析并结合实际生产状况,确定最适合的高温短时固溶处理制度为475 ℃×3 min。采用此制度时锻件45°方向抗拉强度最低,为685 MPa,LT向断后伸长率最低,为4.7%。     

Joint strength of Inconel 718 alloy and its improvement by post-weld heat treatment – joint performance and its controlling factors in friction welding of Inconel 718 alloy

The influences of welding parameters on tensile properties of friction-welded joints of Inconel 718 alloy (subjected to a post-weld heat treatment (PWHT) consisting of a solution treatment at 1253 K and double ageing treatments at 993 and 893 K) have been investigated to reveal the controlling factor of the joint performance. All joints obtained were fractured near the bond interface at smaller elongations and area reductions than the base metal on tensile tests, although most of them showed tensile strengths comparable with that of the base metal. The observations of fractured surface and its cross-sectional microstructure suggested that an interfacial fine grain zone including numerous fine Laves phase particles 30–100 nm in size was responsible for a low ductility fracture at shorter friction time and lower friction pressure. As the friction time and pressure were increased, the fine grain zone disappeared, and a reduction in hardness near the bond interface became significant, causing a rather ductile fracture near the bond interface. With an increase in friction time, coarse Laves phase particles, a few micrometres in size remaining near the bond interface increased and they acted as a crack nucleation site of ductile fracture. An increase in the solution treatment temperature during the post-weld heat treatment enhanced the dissolution of the coarse Laves phase in the low-hardness region, and enabled us to obtain joints that were free from unacceptable grain growth and fractured in the base metal at a solution treatment temperature of 1323 K.     

原位SEM研究LDMD Ti-6Al-4V合金β晶界对拉伸断裂行为的影响

目的研究β晶界对激光直接熔化沉积(LDMD)Ti-6Al-4V合金裂纹形核或传播行为的影响,以澄清合金的断裂机制,为合金性能的改善提供理论依据。方法采用LDMD Ti-6Al-4V合金粉末,在Ti-6Al-4V基板上逐层堆积形成沉积层。沿沉积层扫描方向截取试样,在室温下观察样品的微观组织形貌,并对原位拉伸过程中的微观组织演化进行实时研究。同时研究β晶界对微裂纹萌生、扩展和断裂的影响行为,总结断裂机理。结果 LDMD Ti-6Al-4V合金组织宏观呈现出沿构造方向生长的粗大柱状β晶,β晶内由板条状α晶和整齐排列的具有相同生长取向的α簇组织组成,并有少量孔洞缺陷。采用原位扫描电镜拉伸样品时发现,在横向拉力作用下,样品最初在孔洞周围发生变形,之后裂纹的萌生扩展主要沿β晶界进行,β晶界对拉力起阻碍作用,造成样品的伸长率较低。拉伸过程中,微观组织主要沿着β晶界周围的α相变形,并且孔洞缺陷引起的应力集中使得缺陷周围变形最严重,变形方向与拉力方向呈45°。结论孔洞缺陷决定了样品的初始变形位置,而β晶界则决定了裂纹传播的方向,且由于拉伸试样的截取方向与β晶界相垂直,导致样品的伸长率较低,所以β晶界对样品的力学性能及断裂机理起决定作用。     

3Cr2W8V钢热锻模具淬火开裂原因分析

分析了3Cr2W8V钢热锻模具淬火开裂原因。借助于扫描电镜和光学显被镜，观察断口表面形貌和金相组织，根据断口特征和金相组织找出了模具淬火断裂主要原因是晶粒粗大、碳化物呈带状分布、锻造后未按要求退火细化晶粒，导致模具按正常温度淬火发生断裂。     

快速凝固+热挤压制备Al-10.7Zn-2.4Mg-0.9Cu合金的组织和性能

采用单辊熔体旋转法制备Al-10.7Zn-2.4Mg-0.9Cu合金带材,利用热挤压将带材坯料制成棒材,对其微观组织和力学性能进行研究。结果表明:所制备的带材由过饱和固溶体α(Al)等轴细晶构成,晶粒尺寸为3~5μm;合金经挤压后存在粗大第二相,析出相主要为MgZn2相,挤压态棒材抗拉强度为499.8 MPa,伸长率达到了15.3%,断口呈韧性断裂特征;经T6热处理后,合金中有细小的沉淀相析出,使得室温力学性能得到提高,抗拉强度达到631.9 MPa,伸长率有所降低,断口呈韧脆混合断裂特征。