一种新型镍基高温合金的动态再结晶行为

采用等温热压缩实验研究了一种新型镍基高温合金在不同热变形条件下(变形温度1040～1120℃、应变量0.35～1.2、应变速率0.1 s^-1)的动态再结晶行为。通过光学显微镜(OM)、扫描电子显微镜(SEM)和电子背散射衍射仪(EBSD)研究变形温度和应变量对合金热变形过程中组织演变和动态再结晶(DRX)形核机制的影响。结果表明,根据加工硬化率曲线能够准确确定DRX出现的临界应力和临界应变。合金的DRX晶粒体积分数随变形温度和应变量的增加而增加。在高温低应变速率下,不连续动态再结晶(DDRX)和连续动态再结晶(CDRX)形核机制同时发生。随着变形温度的升高,CDRX形核机制减弱,而CDRX机制在高温条件下占据主导。随着应变量的增加,合金中DDRX机制逐渐变强。热变形后期,CDRX仅作为辅助形核机制发挥作用。另外,Σ3孪晶界的形成有助于DRX晶粒的形核。     

镍基单晶高温合金再结晶过程仿真分析

以DD6镍基单晶高温合金为对象,建立了合金再结晶过程中晶粒形核长大、储能分布的数学模型,利用计算机模拟技术分析了材料热处理过程中再结晶的动力学曲线。模拟结果和文献实验结果具有很高的吻合度,为镍基单晶高温合金蠕变性能的优化提供了参考。     

典型镍基高温合金的再结晶机理

研究了GH4760、GH4738和AD730典型镍基高温合金在热变形过程中的动态和静态再结晶行为,并进行了压缩热变形和固溶退火实验。结果表明,动态和静态再结晶的成核机制以涉及晶界凸起的不连续机理为主。在动态和静态再结晶过程中,普通晶面向低指数晶面转变,产生了不同类型的台阶晶界,这种转变将使更多的晶界具有较低的能量。Σ3晶界上阶梯边界的形貌大多分解为{111}₁/{111}₂和90°{112}₁/{112}₂小平面。台阶状晶界促进了晶界迁移,加速了再结晶过程。再结晶完成后,部分台阶晶界保留,界面能降低,促进了后续晶粒生长。     

粉末粒度对一种新型镍基粉末高温合金热变形行为的影响

利用EBSD、SEM、OM、热模拟试验机等对比研究了不同粉末粒度制备的一种新型镍基粉末高温合金(WZA3)在不同热压缩变形条件下的变形行为和组织差异性。结果表明：相比细粉制备的HIP-01样品而言,粗粉枝晶组织明显,成分偏析严重,其制备的HIP-02样品中残余粗大γ′较多。低温(1050、1080℃)高应变速率(1、0.1s-1)时,HIP-01样品峰值应力值高于HIP-02。热压缩后HIP-01样品边缘开裂情况较HIP-02严重,HIP-01样品保留了大部分原始热等静压组织,裂纹优先在粉末原始颗粒边界(priorparticleboundary,PPB)处产生,HIP-02样品边缘出现了部分再结晶组织。在1080℃/0.001 s^-1时,HIP-02样品峰值应力较HIP-01低约30 MPa,HIP-02样品热压缩过程再结晶现象明显,再结晶晶粒均匀,HIP-01样品出现项链晶组织,再结晶不充分。粗大γ′有利于促进1050和1080℃时HIP-02样品的再结晶。高温(1150℃)、低应变速率(0.001、0.01s^-1)时,γ′全部溶解进基体...     

基于计算机仿真镍基单晶高温合金再结晶过程分析

再结晶是影响高温合金高温蠕变性能的重要因素.以DD6镍基单晶高温合金为研究对象,建立了再结晶过程中形核生长、储能分布、晶粒长大的数学模型,利用计算机模拟技术分析了材料热处理过程中再结晶的整个过程和动力学曲线.该研究为镍基单晶高温合金生产过程中的蠕变性能优化提供了参考.     

镍基粉末高温合金粉末直接锻造技术

镍基粉末高温合金的完全致密化可以通过适当地处理实现,而细化微观组织可以通过再结晶形核实现.本文使用普通液压机且在大气环境下通过粉末直接锻造制备完全致密化的镍基粉末高温合金零件.通过边界取向差测定及分析镍基粉末高温合金零件的再结晶程度.通过Deform-2D/3D有限元软件对粉末直接锻造过程中的实际负载状态进行了模拟验证...     

新型镍基粉末高温合金的热变形行为

采用Gleeble-1500热模拟试验机对新型镍基粉末高温合金FGH98Ⅰ进行了单向热压缩变形试验,研究了其在变形温度为950～1150℃,应变速率为0.0003～1s-1条件下的热变形行为,建立和对比了不同应变量下的应变速率敏感因子m图和功率耗散效率因子η图,并对热加工图进行了组织验证。结果表明:合金的流变应力随着变形温度的升高和应变速率的降低而降低;不同应变量下的η图与m图相似,随着应变量的增大,峰区的η与m值逐渐升高;当真应变为0.5时,在变形温度为1050℃,应变速率为0.0003s-1条件下,η与m达到峰值,分别为40%和25%,合金发生了动态再结晶,晶粒细化且无内裂纹。该结果为FGH98Ⅰ合金实际热加工工艺的优化提供了理论依据。     

镍基粉末高温合金FGH95涡轮盘材料研究

讨论了ＦＧＨ９５氩气雾化粉末高温合金中中缺陷、粉末颗粒凝固组织及其相组成，粉末经过热静压显微组织与相组成、热等静压坯再经包套模锻后合金的组织与低周疲劳性能，以及热等静压坯再再经挤压后合金组织的改善和处理制度的改进。     

NiCoCrAlYTa涂层/镍基单晶高温合金界面再结晶

采用低压等离子喷涂技术在镍基单晶高温合金上制备了NiCoCrAlYTa涂层,通过不同的真空热处理和预处理制度研究其对涂层/镍基单晶界面的影响.结果表明,1080℃真空热处理界面扩散带均产生胞状再结晶体,而1000℃和850℃无再结晶产生.预处理时喷砂压力大于0.2 MPa,在1080℃,6 h热处理后再进行850℃,24 h时效处理界面扩散带均产生再结晶体,无喷砂时无再结晶产生.同时热处理后界面处出现元素的相互扩散及富Ta的Ni2Ta和Cr2Ta相,Ta在胞状晶内偏聚.     

一种铸造镍基高温合金的凝固行为

M963合金的凝固顺序为：L→L γ→L （γ‘ MC） γ→（γ γ‘) （γ MC） γ→（γ γ‘） （γ MC） γ γ‘；凝固组织呈树枝状结构，由γ固溶体基体。γ‘析出组及分布在枝晶间区的骨架状MC碳化物和（γ＋γ‘）共晶组成；碳降低合金的液相线温度和（γ＋γ‘）共晶温度，提高MC碳化物的形成温度，增加MC碳化物的体积分数，降低（γ＋γ‘)共晶的体积分数；高熔点元素W和Co在枝晶干偏聚，Al,Ti,Nb,Cr和Mo在枝晶间偏聚。     

Effect of cooling rate on microstructure and tensile properties of powder metallurgy Ni-based superalloy

The effects of size distribution, morphology and volume fraction of γ′ phase and grain size on tensile properties of powder processed Ni-based superalloy were investigated by using two different quenching methods. Oil quenching and air cooling were adopted with cooling rate of 183 °C/s and 4–15 °C/s, respectively. The experimental results show that the average size of the secondary γ′ after oil quenching is 24.5 nm compared with 49.8 nm under air cooling, and corresponding volume fractions of γ′ are 29% and 34%, respectively. Meanwhile, the average grain size remains nearly equivalent from both oil-quenching and air-cooling specimens. The tensile strength at room temperature is higher for the oil-quenched specimen than the equivalent from the air-cooled specimen, but the difference approaches each other as the temperature increases to 650 °C. The fractography clearly demonstrates that transgranular fracture governs the failure process at ambient temperature, in contrast to the intergranular fracture at 650 °C or even higher temperature. These two mechanical responses indicate the strengthening effects of γ′ precipitates and grain boundary for polycrystalline Ni-based superalloys at different temperatures.     

一种新型镍基粉末高温合金的热压缩性能研究

基于Gleeble热压缩模拟试验,研究变形温度和应变速率对一种新型第三代镍基粉末高温合金WZ-A3挤压态试样在变形温度1040~1130 ℃区间,应变速率0.01~0.0025 s_^-1 条件下的热压缩变形行为,分析了合金在不同热压缩条件下的晶粒尺寸及显微组织的变化。试验结果表明：WZ-A3合金挤压棒在1070~1100 ℃温度范围, 0.01~0.005 s_^-1 应变速率范围内热压缩变形后可以获得约4.5 μm细小均匀的晶粒组织,各部位均未出现项链晶及异常晶粒长大的现象。根据以上试验条件成功制备了两件直径190 mm高97 mm的小尺寸热模锻试验盘,验证了WZ-A3合金的热压缩性能。     

FGH96合金动态再结晶行为的研究

利用Gleeble-1500热模拟试验机对FGH96合金在不同热变形制度下的动态再结晶行为进行了研究。结果表明:在较高应变速率下(>2×10-3s-1),合金流变曲线呈明显的动态再结晶特征,低应变速率下(5×10-4s-1)呈现明显的动态回复特征;变形温度、应变速率和应变量对获得细晶组织都有重要的影响,但应变速率对动态再结晶晶粒大小影响最为显著,动态再结晶晶粒的平均晶粒尺寸大小-D与Z参数满足如下关系:ln-D=7.617-0.0134lnZ;利用加工硬化率和应变的关系曲线确定了该合金的稳态应变sε,建立了该合金的动态再结晶状态图。     

Phase precipitation behavior and tensile properties of as-cast Ni-based superalloy during heat treatment

The phase precipitation behavior and tensile properties of an as-cast Ni-based alloy, IN617B alloy, after solution heat treatment and long-term aging treatment were investigated. Ti(C,N), M₆C and M₂₃C₆ are the primary precipitates in as-cast microstructure. After solution heat treatment, most of carbides dissolve into the matrix except a few fine Ti(C,N) within grains. During long-term aging at 700 °C, the phase precipitation behaviors of the alloy are characterized as follows: (1) M₂₃C₆ carbides at grain boundaries (GBs) transform from film-like shape to cellular shape and gradually coarsen due to the decrease of the surface energy and element aggregation to GBs; (2) M₂₃C₆ carbides within grains have a bar-like morphology with a preferential growth direction [110] and have a cube-on-cube coherent orientation relationship with the matrix γ; (3) γ′ particles inhibit the coarsening of M₂₃C₆ within grains by constraining the diffusion of formation elements. Furthermore, the tensile strength of the alloy obviously increases, but the ductility significantly decreases after the aging for 5000 h. The alloy has a relatively stable microstructure which guarantees the excellent tensile properties during long-term aging.     

热等静压处理温度对一种高性能粉末高温合金组织和性能的影响

采用光学显微镜、扫描电镜和拉伸试验等研究了不同温度热等静压处理(HIP)对一种高性能粉末高温合金显微组织和力学性能的影响。结果表明:在γ′相溶解温度以下进行热等静压处理,合金中存在较多的原始粉末颗粒边界(PPB)组织,并且含有大量的残留枝晶,热处理后PPB不能完全消除,以至于影响合金的室温和高温塑性;在γ′相溶解温度以上进行热等静压处理,基本消除了PPB组织,残留枝晶含量较少,热处理后得到完全再结晶组织,不含有PPB组织,同时晶粒并未快速长大。     

Room temperature tensile deformation behavior of a Ni-based superalloy with high W content

K416B Ni-based superalloy with high W content has good high temperature properties and low cost, which has a great development potential. To investigate the room temperature tensile property and the deformation feature of K416B superalloy, tensile testing at room temperature was carried out, and optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the deformation and damage mechanisms. Results show that the main room temperature tensile deformation features of the K416B nickel-based superalloy are dislocations slipping in the matrix and shearing into γ′ phase. The <110> super-dislocations shearing into γ′ phase can form the anti-phase boundary two coupled (a/2)<110> partial-dislocations or decompose into the configuration of two (a/3)<112> partial dislocations plus stacking fault. In the later stage of tensile testing, the slip-lines with different orientations are activated in the grain, causing the stress concentration in the regions of block carbide or the porosity, and cracks initiate and propagate along these regions.

     

Rapid manufacture of Ni-based superalloy components by three-dimensional printing

The challenge to rapid manufacturing high performance metal components is how to consolidate the uncompressed powder preforms to full or near full density without shape distortion. A new approach developed by ProMetal was proposed, in which a bimodal powder, typically a coarse prealloyed powder blended with a fine metal powder was used to build green preforms by three-dimensional printing and then sintered at a temperature above the solidus temperature of the coarse prealloyed powder and below the melting temperature of the fine powder particles or the solidus temperature if the fine powder is a prealloyed powder as well. This approach was successfully applied to sinter Ni-based superalloy 718 preforms, which were built through three dimensional printinginto near full density.