粉末高温合金FGH96中的原始粉末颗粒边界及其对合金拉伸断裂行为的影响

采用等离子电极旋转雾化法和热等静压法(hot isostatic press,HIP)分别制备FGH96粉末与合金,对原始及高温(1 150℃)预热处理后的FGH96粉末表面析出相以及HIPed FGH96合金的原始粉末颗粒边界(prior particleboundary,简称PPB)进行分析,进而研究PPB对合金室温和750℃拉伸断裂行为的影响。研究发现:原始粉末表面无明显析出相,1 150℃预热处理后粉末表面有块状MC和细小氧化物分布;热等静压法制备的FGH96合金及其热处理后,PPB析出相主要由颗粒和块状的金属碳化物MC及富Zr的氧化物颗粒组成;该合金经过固溶和时效处理后,颗粒状MC部分溶解而块状MC长大,PPB碳化物的尺寸分布由单峰分布转变为双峰分布;常温拉伸时微孔在PPB上形成并扩展,合金沿PPB断裂;750℃拉伸时,合金强度与塑性较常温下明显降低,部分M23C6在晶界析出,块状和颗粒状碳化物部分溶解,为M23C6提供碳源,合金断口呈现沿晶和沿PPB混合断裂的形貌。     

FGH96合金原始颗粒边界(PPB)及其对冲击性能的影响

对Ar雾化(AA) FGH96合金的原始粉末颗粒表面、热等静压(HIP)和HIP+热处理(HT)后的合金断口分别进行俄歇电子能谱(AES)分析,并利用金相显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)对HIP态合金及HIP+ HT态合金进行组织观察.结果表明:HIP态合金的PPB析出相主要由MC型碳化物和尺寸为1～5μm的大γ相所组成;HIP态合金的夏比冲击断口是沿着PPB的位置断裂的,而HIP+ HT态合金的冲击断口的断裂方式是穿晶断裂,呈韧-脆混合断裂的形式;HIP+ HT态合金基本消除了PPB缺陷组织,冲击性能得到明显提高.     

碳含量对热等静压FGH4169合金原始颗粒边界与力学性能的影响

用3种不同碳含量的GH4169合金粉末为原料,采用粉末热等静压+热处理工艺制备碳含量(质量分数,下同)分别为0.026%,0.045%和0.078%的FGH4169合金,研究碳含量对FGH4169合金PPB(prior particle boundary,原始颗粒边界)和力学性能的影响。结果表明,随碳含量从0.026%增加到0.078%,FGH4169合金析出碳化物增多,超过0.078%后,形成PPB;FGH4169合金中碳化物主要为富Ti和Nb的MC型碳化物,但碳含量对合金中碳化物的种类及形貌没有明显影响;在一定碳含量范围内,随碳含量增加,FGH4169合金基体上析出的γ'相数量减少,且碳化物越来越趋向于在原始颗粒边界聚集,导致合金的室温和650℃高温强度和塑性逐渐减小。     

粉末预热处理对HIP Rene‘95粉末高温合金组织的影响

本文研究了Rene′95合金粉末经不同温度预热处理再热等静压(HIP)后合金原始颗粒边界(PPB)碳化物析出、γ′含量及晶粒度的变化;探讨了采用粉末预处理方法减少HIP Rene′95合金PPB碳化物聚集的可能性。结果表明:预处理可以明显改善HIP Rene′95合金PPB碳化物的聚集程度,并且增加合金γ′含量而不改变合金的晶粒度。指出,这是由于预处理改善了HIP前粉末颗粒的表面状态,改变了碳化物在PPB的形核条件所致。     

消除粉末高温合金中原始颗粒边界机制

采用SEM、TEM研究了高温合金粉末颗粒内部与合金中碳化物的类型和组成,采用热力学软件计算了不同Hf含量FGH4096的碳化物组成,结果表明,粉末高温合金中原始颗粒边界上的析出物为以TiC为主的MC型碳化物,MC型碳化物(TiC、ZrC、HfC、NbC、TaC)在镍基高温合金中按溶解度从大到小为TiCNbCTaCZrCHfC。TiC在FGH4096中的溶解度较HfC的大,雾化粉末快速凝固过程中,加入Hf的FGH4096合金碳化物析出量大于不加Hf的FGH4096合金碳化物析出量,HfC均匀形核于整个粉末颗粒中。在热等静压过程中,Hf与C的结合力强而形成HfC,最终在FGH4096合金中形成(Hf,Ti,Nb)C,致使C元素无法扩散至粉末颗粒表面形成TiC,避免了原始粉末颗粒边界的形成。加入Zr消除FGH4096中原始颗粒边界的机制与添加Hf的FGH4096相同。     

消除粉末高温合金中原始颗粒边界机制北大核心

采用SEM、TEM研究了高温合金粉末颗粒内部与合金中碳化物的类型和组成,采用热力学软件计算了不同Hf含量FGH4096的碳化物组成,结果表明,粉末高温合金中原始颗粒边界上的析出物为以TiC为主的MC型碳化物,MC型碳化物(TiC、ZrC、HfC、NbC、TaC)在镍基高温合金中按溶解度从大到小为TiC>NbC>TaC>ZrC>HfC。TiC在FGH4096中的溶解度较HfC的大,雾化粉末快速凝固过程中,加入Hf的FGH4096合金碳化物析出量大于不加Hf的FGH4096合金碳化物析出量,HfC均匀形核于整个粉末颗粒中。在热等静压过程中,Hf与C的结合力强而形成HfC,最终在FGH4096合金中形成(Hf,Ti,Nb)C,致使C元素无法扩散至粉末颗粒表面形成TiC,避免了原始粉末颗粒边界的形成。加入Zr消除FGH4096中原始颗粒边界的机制与添加Hf的FGH4096相同。     

粉末氧含量对热等静压FGH4169合金力学性能与组织的影响

以氧含量分别为60×10~(-6),145×10~(-6)和216×10~(-6)的GH4169预合金粉末为原料,采用粉末热等静压法制备成块体合金,然后进行热处理,研究粉末氧含量对FGH4169合金的室温和高温力学性能及组织的影响。结果表明,随原始粉末氧含量从60×10~(-6)增加到216×10~(-6),Al和Ti元素在粉末表面富集,并生成斑点状氧化物;粉末氧含量对FGH4169合金的致密度无明显影响,但可改变合金中碳化物的分布和形态。高氧含量的FGH4169合金中易形成原始颗粒边界(prior particle boundary,PPB),PPB中含有碳化物和氧化物。FGH4169合金在室温和高温下的塑性均随氧含量增加而降低,粉末氧含量为60×10~(-6)和145×10~(-6)时,FGH4169合金在室温和650℃下的强度和塑性都能达到变形GH4169合金的标准值。     

微量元素Hf消除FGH96合金中原始粉末颗粒边界组织机制的探讨

粉末冶金高温合金中原始粉末颗粒边界组织(PPBS)由碳化物和少量碳氧化物组成。采用SEM、TEM以及AES等研究了粉末颗粒内、表面上以及合金中PPB上碳化物的结构和组成,依据热力学和扩散理论分析了Hf消除原始粉末颗粒边界组织(PPBS)的微观机制。结果表明:快速凝固粉末颗粒表面形成含有Ti、Nb、Cr、Mo、W的MC型亚稳定碳化物MC′,在HIP过程中粉末颗粒表面上的MC′相转变成稳定的MC相,以及粉末颗粒内的Ti、C元素向烧结颈处扩散,HIP后在粉末颗粒边界上形成富Ti和Nb的MC型碳化物(Ti,Nb)C。加入微量Hf后,在粉末颗粒内形成了更多更稳定的含Hf的MC型碳化物(Ti,Nb,Hf)C,C、Ti被"绑定"在碳化物(Ti,Nb,Hf)C中,抑制了C、Ti向烧结颈处扩散,从而抑制了MC型碳化物在粉末颗粒边界上的析出。     

氩气雾化法制备FGH96高温合金粉末颗粒的凝固组织

利用扫描电镜(SEM)对氩气雾化(argon gas atomization,缩写AA)工艺制备的FGH96高温合金原始粉末颗粒的粘结形式、凝固组织、表面和内部形貌及其形成机理进行研究.结果表明:AA法制备的FGH96合金粉末,在颗粒尺寸d≥40 μm时,颗粒之间出现凸起式粘结、包覆式粘结以及葫芦式粘结,其中凸起式粘结...     

FGH95粉末高温合金原始颗粒边界及其对性能的影响

本文针对FGH95合金中原始颗粒边界的组成及其对合金冲击韧性、拉伸性能和持久性能的影响进行了研究。研究结果表明:其原始颗粒边界的组成与粉末的氧含量有很密切的关系。当氧的含量低于40×10-6时,原始颗粒边界主要由大尺寸γ′组成,这种原始颗粒边界不会对合金的力学性能产生影响;当氧的含量大于70×10-6时,原始颗粒边界主要由MC型碳化物组成,这种原始颗粒边界将对合金的力学性能产生不利影响。     

Study of Metallic Carbide (MC) in a Ni-Co-Cr-Based Powder Metallurgy Superalloy

The evolution of carbides in a Ni-Cr-Co-based powder metallurgy (PM) superalloy in the as-atomized, as-atomized + annealed, hot isostatic pressed (HIPed) and HIPed + annealed conditions were systematically analyzed to understand the formation of blocky metallic carbide (MC) along the previous particle boundary (PPB). The results show that the carbides both on the powder surfaces and in the bulk of the powder particles are mainly fan-shaped MC whose decomposition temperatures are in the range of 1473 K to 1493 K (1200 °C to 1220 °C). PPB carbides in the HIPed alloy are mainly block-shaped MC, and the fan-shaped MC densely distributed in the area that have not been consumed by the recrystallized grains. The formation mechanism of PPB carbides can be described as follows: When the powders are HIPed at 1453 K (1180 °C), the fan-shaped carbides are decomposed at the migrating boundaries of recrystallized grains, and the preferential precipitation of block-shaped MC at PPB is promoted by the carbide-forming elements released by the fan-shaped carbides. When the HIPed alloy is annealed at 1453 K (1180 °C), the area fraction of PPB carbides increases with an increase in annealing time but that of the fan-shaped carbides exhibits opposite behavior. This proves the above formation mechanism of PPB carbides.     

Microstructure Characterization and Mechanical Properties of FGH 95 Turbine Blade Retainers

FGH 95 is a powder metallurgy (P/M) processed superalloy,which was developed in the 1980s in China.One of the applications of FGH 95 was high pressure turbine blade retainers.The manufacturing processes used to produce FGH 95 blade retainers consisted of atomization by plasma rotating electrode process (PREP),hot isostatic pressing (HIP) at super-solvus temperature and a sub-solvus solution heat treatment.The material had an equiaxed grain structure (ASTM 6.5-7.5).The γ′ precipitates in as-HIP FGH 95 showed a tri-model distribution.Carbides in the alloy were MC type and precipitated at grain boundaries.The prior particle boundaries (PPB) in the material originated mainly from γ′ phase.Statistics of the mechanical properties data from batch production of the FGH 95 blade retainers were investigated.The as-HIP FGH 95 blade retainers showed high strength at room temperature and 650 ℃,excellent creep resistance and outstanding stress rupture strength at 650 ℃.     

C元素对FGH96粉末高温合金显微组织和力学性能的影响

对C质量分数分别为0.05%和0.09%的FGH96合金进行了显微组织和力学性能的分析。结果发现:C元素含量较高时,除了碳化物数量明显增多外,还会在晶界处形成较大尺寸的块状MC碳化物;但是,C元素含量并未对原始颗粒边界(prior particle boundary,PPB)、晶粒度及γ′相产生明显的影响。C元素含量较高会提高FGH96合金在650℃时的抗拉强度和屈服强度,但会降低其塑性。在低周疲劳试验中,C元素含量较高,形成的大块MC型碳化物分布于表面或亚表面,将会作为裂纹起源从而显著降低合金的低周疲劳性能。     

含Hf镍基粉末高温合金快速凝固粉末颗粒特性

采用扫描电镜、透射电镜及其附带的能谱仪和碳复型萃取技术等多种手段研究了不同Hf含量的FGH96合金粉末颗粒显微组织、枝晶间合金元素偏析和析出相.发现Hf含量可以改变粉末颗粒内部树枝晶、胞状长大晶和微晶凝固组织的比例,粉末的快速凝固组织形态主要取决于冷却速率和固液界面前沿温度梯度与长大速度的比值.不同Hf含量的FGH96合金粉末颗粒中,Nb、Ti、Zr和Al均富集于枝晶间,Co、Cr、W和Ni均富集于枝晶轴.当Hf质量分数为0.3%时,Ti、Nb、Zr、Hf等强碳化物形成元素的枝晶偏析程度最小.在快速凝固粉末颗粒中,Hf对氧含量比碳含量更敏感,优先形成更稳定的氧化物HfO₂.      

镍基粉末高温合金枝晶间亚稳碳化物

对急冷凝固镍基高温合金松散粉末热等静压成型合金中亚稳碳化物及其相间反应进行了研究.随着热处理温度的升高,粉末中合金元素的分布逐渐均匀化,但枝晶间MC能在较高的温度下保持稳定,使Ti和Zr在该处仍有较高含量.原始粉末中枝晶间主要分布着块状和花状的MC型碳化物,在预热处理过程中粉末枝晶间块状碳化物分解,发生M₂₃C₆和M₆C的析出反应,而花状碳化物的成分及形貌则保持相对稳定.成型合金残余枝晶间分布的碳化物主要由块状M₆C和MC及花状MC组成,形变再结晶可以促进枝晶间碳化物的溶解.      

Microstructure,Tensile Properties,and Hot-Working Characteristics of a Hot Isostatic-Pressed Powder Metallurgy Superalloy

A series of microstructure observation, tensile, and hot compression tests were conducted to investigate the variation of microstructure, tensile properties, and hot-working characteristics of a powder metallurgy (PM) superalloy with hot isostatic pressing (HIPing) temperature, to establish a basis for the parameter selection for PM superalloy preparation. The results show that the dendritic structure from the powder was not completely removed until the HIPing temperature is above the γ′ solvus; γ/γ′ eutectic formed when the powder particles were HIPed at 1533 K (1260 °C) or above. Prior particle boundaries (PPBs) were observed in alloys HIPed at 1513 K (1240 °C) and below; the PPB decoration is serious in alloys HIPed at 1483 K and 1513 K (1210 °C and 1240 °C), owing to melting and aggregation of the boride phase at the particle boundaries during HIPing; the PPBs were eliminated when the HIPing was done at 1533 K (1260 °C) or above. Tensile fracture mode of the alloy changes from inter-particle and transgranular mixed fracture to transgranular fracture with increasing HIPing temperature, which is in accordance with the change in precipitate distribution at the PPBs. The hot workability of alloy is poor for all combinations of HIPing/deformation conditions except for HIPing at sub-solvus temperature and deformation at low strain rates.

     

热变形对FGH96高温合金原始颗粒边界的影响

通过Gleeble-1500热模拟试验机对热等静压成形FGH96高温合金进行热压缩试验,其中温度为1075℃,变形速率为0.001 s-1,变形量为70%。利用场发射扫描电镜、透射电镜和电子能谱研究了合金原始颗粒边界（prior particle boundary,PPB）的组成,讨论了原始颗粒边界在FGH96高温合金再结晶过程中的作用,并分析了合金热变形对原始颗粒边界的影响。结果表明:热等静压成形FGH96高温合金中的原始颗粒边界主要由Ti的碳化物和γˊ相共同组成;原始颗粒边界对合金热变形再结晶形核起促进作用,对晶粒长大起阻碍作用;合金热变形可以改善原始颗粒边界在组织中的分布,从而使晶粒长大过程顺利进行。     

Powder metallurgy T15 tool steel: Part I. Characterization of powder and hot isostatically pressed material

The microstructure and constitution of T15 tool steel processed from gas-atomized powder have been characterized. From the atomized powder, four particle size ranges (≤840, 250 to 840, 44 to 100, and ≤44 Μm) were consolidated to full density by hot isostatic pressing (“hipping”) at 1130 ‡C or 1195 ‡C. Both atomized powder and consolidated material were examined by means of optical and electron microscopy, X-ray diffraction, chemical analysis, and micro-hardness. A segregated structure exists in the gas-atomized powder, independent of particle size; MC and M₂C carbides are present, primarily at cell boundaries. The matrix of the powders is a mix of martensite and retained austenite. Weight fraction and overall composition of the carbides are insensitive to particle size, but the proportion of MC carbides increases with decreasing particle size. After consolidation, MC, M₆C, and M₂₃C₆ carbides are present in a ferrite matrix. The carbide size distribution is skewed to larger carbide sizes at the higher consolidation temperature, independent of the prior particle size fraction, but there is no significant change in carbide volume fraction. For a given consolidation temperature, the size distribution of the MC and M₆C carbides is broader for the coarser particle size fractions.     

气体雾化快凝W9高速钢粉末的组织特征

研究了颗粒粒度不同的气体雾化W9Mo3Cr4V高速钢粉末的组织、形貌及结构.结果表明:粉末由铁素体和奥氏体基体和分布在周围的MC及M2C型碳化物组成,基体组织为等轴晶及树枝晶,碳化物在空间上呈连续网状或树枝状分布;粉末中相的含量与粉末粒度相关,随高速钢粉末粒度减小,组织中的铁素体和MC型碳化物含量增加,奥氏体和M2C型碳化物含量减少.     

Effect of Density and Processing Conditions on Oxide Transformations and Mechanical Properties in Cr–Mo-Alloyed PM steels

To improve the mechanical properties and performances of water-atomized powder metallurgy steels, it is necessary to enhance the density. Consolidating water-atomized steel powders via conventional pressing and sintering to a relative density level > 95 pct involves processing challenges. Consolidation of gas-atomized powders to full density by hot isostatic pressing (HIP) is an established process route but utilizing water-atomized powders in HIP involves challenges that result in the formation of prior particle boundaries due to higher oxygen content. In this study, the effect of density and processing conditions on the oxide transformations and mechanical properties from conventional press and sintering, and HIP are evaluated. Hence, water-atomized Cr–Mo-alloyed powder is used and consolidated into different density levels between 6.8 and 7.3 g cm⁻³ by conventional die pressing and sintering. Fully dense material produced through HIP is evaluated not only of mechanical properties but also for microstructural and fractographic analysis. An empirical model based on power law is fitted to the sintered material properties to estimate and predict the properties up to full density at different sintering conditions. A model describing the mechanism of oxide transformation during sintering and HIP is proposed. The challenges when it comes to the HIP of water-atomized powder are addressed and the requirements for successful HIP processing are discussed.