Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.

Effect of the capsule on deformation and densification behavior of nickel-based superalloy compact during hot isostatic pressing

The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing(HIP) was modified through uniaxial compression experiments. The influence of cylindrical capsule characteristics on FGH4096M superalloy powder compact deformation and densification behavior during HIP was investigated through simulations and experiments. Results revealed the simulation shrinkage prediction fitted well with the experimental shrinkage including a maximum shrinkage error of 1.5%. It was shown that the axial shrinkage was 1.7% higher than radial shrinkage for a cylindrical capsule with the size of ∮50 mm × 100 mm due to the force arm difference along the axial and radial direction of the capsule. The stress deviated from the isostatic state in the capsule led to the uneven shrinkage and non-uniform densification of the powder compact. The ratio of the maximum radial displacement to axial displacement increased from0.47 to 0.75 with the capsule thickness increasing from 2 to 4 mm. The pressure transmission is related to the capsule thickness, the capsule material performance, and physical parameters in the HIP process.

Deformation Behavior of Hot Isostatic Pressing FGH96 Superalloy

The deformation behavior of hot isostatic pressing （HIP） FGH96 superalloy was characterized in the temperature range of 1000-1100 ℃ and strain rate range of 0. 001-0. 1 s^-1 using hot compression testing. The flow curves of HIP FGH96, superalloy during hot deformation was analyzed systematically. The results show that deformation temperature, strain rate and strain are the main influence factors on flow stress of HIP FGH96 superalloy during hot deformation. The flow stress displays a peak at a critical strain and then decreases with further increase in strain. For a given strain, the flow stress decreases with the increase of deformation temperature, and increases with the increase of strain rate. A mathematical model of these flow curves was established through regression analysis and taking the strain as a modification factor. The calculated stress values agree well with the experimental values.

Microstructure and mechanical properties of CuAgZn/GH909 diffusion bonded joint fabricated by hot isostatic pressing

The hot isostatic pressing-diffusion bonding(HIP-DB)was proposed to achieve the joining of CuAgZn and GH909 directly without an interlayer.The microstructure of joint was characterized by scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).The microhardness and shear strength were tested to investigate the mechanical properties of joint.The results showed that the interface was complete,and the joint was compact,uniform and free of unbonded defects.The maximum microhardness of joint was HV 443,higher than that of two base alloys,and the average shear strength of joint reached 172 MPa.It is concluded that a good metallurgical bonding between CuAgZn and GH909 can be obtained by HIP-DB with the process parameters of 700℃,150 MPa and 3 h.

Combining Aluminum Heat Treat with Hot Isostatic Pressing: A Comparison of Structure, Properties, and Processing Routes for a Cast AI-Si-Mg Alloy

Bodycote researchers have successfully demonstrated that a T6 heat treatment can be integrated with Densal?, a proprietary, aluminum specific, hot isostatic pressing (HIP) process. In this combined operation, at least a portion of the solution heat treatment is conducted at elevated pressure. During development, two issues, adiabatic cooling during depressurization and a possible variation in the kinetics of homogenization resulting from conducting the solution heat treat at elevated pressure were perceived as factors which could alter the heat treat response from that seen in conventional processing. This paper reviews the results of experiments performed to Al-Si-Mg (A356.0) castings subjected to both combined and conventional processing routes. Results indicate that the combined HIP and heat treat process is an efficient means of achieving a microstructure characteristic of a conventionally T6 processed material while eliminating porosity within the casting. Further, the fatigue life of an A356.0 casting processed using the combined cycle can be improved by more than an order of magnitude over the as-cast and T6 treated component.

Simulation of pressure effects on hot isostatic pressing of stainless steel powder

To investigate the effects of pressure on the hot isostatic pressing(HIP) process of a stainless steel powder,density distribution and deformation of the powder at four different applied pressure levels were predicted and compared by using finite element method(FEM).Constitutive relations of porous compacts during HIP process were derived based on the yield criterion of porous metal materials.Thermo-mechanical coupling calculations were carried out by the MSC.Marc.Densification mechanisms were studied through evolutions of relative density,equivalent plastic strain and equivalent viscoplastic strain rate for compacts.The simulation results were also compared with experimental data.The results show that the densification rate and final density of compacts increase dramatically with the increase in the applied pressure level when it is below 100 MPa during HIP process,and the creep for compacts evolves into steady stage with the improvement of density.

Healing Process of Casting Pores in a Ni-based Superalloy by Hot Isostatic Pressing

Hot isostatic pressing （HIP） with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy （Mgl） turbocharger blade to explore the healing process of casting pores generated during investment casting. Optical micrograph and scanning electron naicroscopy （SEM） observations indicate that eutectic pores are the main cast defects in the as-cast blade before HIP. These pores normally locate at the solidification front of γ/γ＇ eutectic with a size of a few micrometers to a few tens of micrometers. After HIP for 4 h, most of the pores were closed. Based on phase characteristics, these pores were healed by the formation of γ matrix with finer and irregular-shaped γ＇ precipitates. Healing interface can be easily distinguished by SEM. Line scan by using energy dispersive X-ray spectroscopy （EDS） reveals a much higher Ti and Al concentration in the healing interface. It is proposed that solute diffusion toward the casting pores during HIP results in the formation of γ, and the much higher concentration of γ＇-forming elements Al and Ti near the healing interface contributes to the precipitation of γ＇ in the healed region in the succeeding cooling process after HIP.

Microstructural Evolution of Creep-Induced Cavities and Casting Porosities for a Damaged Ni-based Superalloy Under Various Hot Isostatic Pressing Conditions

The microstructural evolution of casting porosities and creep-induced cavities for a damaged nickel-based superalloy under different hot isostatic pressing （HIP） conditions was investigated in order to understand the effects of HIP parameters on the healing behavior of micropores. A number of small-sized creep cavities formed during long-term service and large-sized porosities formed during the casting process were observed. These microdefects were partially healed after treated at high temperature of 1100 ℃ combined with 150 MPa pressure for 2 h, together with the formation of the so- called concentrically oriented γ rafting structure. When HIP temperature was increased to 1150 and 1175 ℃, both the amount and the size of the microdefects were decreased. The concentrically oriented γ rafting around creep cavities became more remarkable, and the primary γ denuded zone was also formed between the raft structure and the cavity. Energy-dispersive X-ray spectroscopy analysis revealed that the γ matrix solute atoms diffused toward the cavity under the concentration gradient, whereas the γ-forming elements diffused in a negative direction. When increasing HIP temperature up to 1200 ℃, the micropores were hardly observed, indicating that both casting porosities and creep-induced cavities had almost been healed. Meanwhile, theγ rafting structure disappeared since HIP temperature was beyond theγ solvus temperature. It is revealed by the experimental results that the atomic diffusion could mainly dominate the healing process of micropores.

高温HIP对难熔金属显微组织与性能的影响

使用1800℃的高温HIP,研究了纯钨、钨镧、TZM和MHC等材料的微观组织和力学性能。试验发现:经过HIP1800处理后,钨镧合金的晶粒未发生明显变化,硬度高于纯钨;去应力状态的TZM和MHC钼合金性能差异在经过HIP1800后得到了消除,具有相似的显微组织和室温力学性能。

Effect of solution heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Hastelloy X manufactured by electron beam powder bed fusion

Prior to the application of AM components for critical applications,it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts.In this study,efforts were made to achieve an in-depth understanding of the effect of post-fabrication Solution Heat Treatment(SHT)and Hot Isostatic Pressing(HIP)on the microstructure and mechanical properties of Hastelloy X parts built by electron beam powder bed fusion(PBF-EB)process.The effects of SHT and HIP on porosity,microstructure,texture and mechanical properties have been investigated and compared with that of as-built PBF-EB Hastelloy X.Post-fabrication HIP treatment led to a significant reduction in the porosity content,whereas no notable difference in porosity was observed between SHT and as-built parts.There was no evidence of any recrystallization occurring following the post-fabrication treatments as elongated columnar grain structures observed within as-built part were found to be maintained even after SHT and HIP process alongside the strong<100>crystallographic texture.Emphasis was laid upon understanding the influence of SHT and HIP on mechanical properties through stress-strain curves and work-hardening behaviour.

热等静压(HIP)技术在金属材料方面的应用

本文对北京’９９ 国际热等静压会议有关论文中提到的热等静压技术的新应用及新的研究动向进行了评述。文章共分四个部分， 即热等静压技术在钛合金、高温合金、铍材以及难熔金属等方面的应用。

大型粉末冶金/热等静压(PM HIP)产品:一个增长有望的产业

用热等静压能生产出用任何其他工艺无法生产的大型粉末冶金产品,大型的HIP(热等静压)装置能制造非常大的零件。大型粉末冶金/热等静压产品(以下简称PM HIP)装置为产业带来了新的机会。ZMet Inc的Dr Stephen J Mashl在为Powder Metallurgy Review撰写的这篇独家报告中,概述了HIP装置的发展,并估计了大型粉末冶金产品的生产潜力。

提高我国高压超高压液压件铸件质量的必备设备(HIP)热等静压机

该文对工程机械的变量柱塞泵、整体式多路阀的零件特别是较复杂的铸件进行了研究,对解决铸件微小气孔的(HIP)热等静压机进行了研究。通过国际、国内对航空航天、军工用的高压、超高压液压件铸件普遍采用HIP技术处理的情况得出结论:我国对液压件铸件进行攻关时,仅偏重材料的化学成分是不够的,应把铸件处理设备和HIP设备作为必备设备,则高压、超高压液压件铸件才能真正过关。

HIP-NNs法制造铍光学镜体

讨论了直接热等静压至近净形(HIP-NNS:Hot lsostatic Pressing to Near-Not-Shape)工艺在铍光镜制造中的应用。HIP-NNS工艺具有快速一步成形、机加工量小、成本低等优点,尤其适用于昂贵、质脆、剧毒铍这一特殊材料的固结。与传统真空热压法相比,由该工艺制得的单块轻型网状铍光镜消除了热膨胀系数的各向异性和不均匀性,从而进一步促进铍光镜的广泛应用。

直接HIP成型粉末高温合金中PPB问题研究的介绍

原始粉末颗粒边界(PPB)是粉末高温合金中存在的主要缺陷之一,它是热等静压(HIP)过程中由于元素偏析与表面吸附的氧和碳发生化学反应形成了以向粉末颗粒边界聚集为特征的一层网状析出相。PPB的存在阻碍金属颗粒间的扩散与连接,使粉末颗粒之间无法进行充分的冶金结合,形成弱界面,降低了合金的力学性能。本文分析了PPB形成及评价方法方面的相关研究,综述了PPB对直接HIP成型粉末高温合金组织和性能影响的相关研究进展,并介绍了一些预防和消除PPB的主要方法。

材料损伤HIP自愈合机理研究

目的研究金属注射成形烧结后内部缺陷自愈合方法。方法将热等静压(HIP)技术与金属注射成形(MIM)工艺结合,控制热等静压参数使得注射成形烧结后的内部缺陷产生自愈合。借助扫描电镜观察内部孔隙消除与缺陷的闭合情况,通过CAE仿真分析颗粒间应力变化,研究热等静压工艺(HIP)自愈合的机理,通过力学抗压试验测试HIP后力学性能。结果扫描电镜结果表明,内部孔隙与缺陷在HIP后完全消除,CAE结果表明,HIP自愈合过程主要是高温高压下的材料发生塑性变形流动机制与扩散蠕变机制起主导作用。力学性能结果表明,HIP后抗压强度提升21.47%,屈服强度提升28.91%,并且HIP后应变断裂点数值明显小于热等静压前。催化进度过程中,粉体内部聚甲醛气体分解挥发后,在零件的内部会形成多孔性结构,并且气体逃逸的通道形成了裂纹,造成烧结过程中厚壁件内部形成空隙与裂纹。结论热等静压后由金属注射成形烧结后形成的内部缺陷完全消除。随着研究的深入和完善,可为金属粉末成形零件的性能优化和广泛应用提供基础。

Ti_(2)AlNb合金粉末热等静压成形的组织和性能

分别采用等离子旋转电极雾化法(Plasma rotating electrode process,PREP)和无坩埚感应熔炼超声气体雾化法(Electrode induction melting gas atomization,EIGA)制备了Ti_(2)AlNb洁净预合金粉末,并对预合金粉末进行了表征。通过热等静压(Hot isostatic pressing,HIP)工艺制备了Ti_(2)AlNb合金,研究了制粉工艺对Ti_(2)AlNb合金显微组织与力学性能的影响。试验结果表明,与PREP法相比,EIGA法制备的Ti_(2)AlNb粉末振实密度更高;基于粉末热等静压近净成形技术,在1030℃/140 MPa/3 h的条件下开展了Ti_(2)AlNb叶轮的成形研究,有限元模拟结果显示,粉末振实密度越高,部件热等静压后变形程度越小,综合考虑构件成形,优选振实密度更高的EIGA制粉工艺制备Ti_(2)AlNb粉末合金复杂部件。

热等静压对一种激光增材制造镍基高温合金组织与性能的影响

以ZGH451合金为研究对象,利用OM、SEM、EBSD等手段研究了热等静压前后的微观组织和力学性能。结果表明,经热等静压工艺处理后,ZGH451合金试样熔池消失,微观组织仍为柱状晶,晶粒尺寸和方向基本和沉积态试样保持一致,未出现再结晶和晶粒长大现象。合金显微缺陷大量减少,微孔体积分数由0.226 5%下降至0.000 512 5%,有效直径由80μm下降至13.5μm。随着热等静压处理温度的升高,位错密度逐渐降低。经热等静压工艺处理后,残余应力从拉应力变为压应力,抗拉强度未发生明显改变;维氏硬度和断后拉伸率大幅上升,HIP1180工艺处理的ZGH451合金维氏硬度从HV 411上升至HV 430,增加了4.7%;断后伸长率提高了35.29%。经过合适的热等静压工艺处理后,使ZGH451合金获得了良好的拉伸性能。

铸造镍基高温合金K417G中高温拉伸断裂机理研究

研究了高温合金K417G热等静压热处理后700℃和950℃时拉伸的断裂机制,使用万能试验机进行中高温拉伸试验,通过扫描电子显微镜对组织、断口形貌、断口纵截面进行观察。结果表明:热处理后试样枝晶形貌明显,枝晶干上γ′相立方度较高,尺寸为0.4~0.5μm,且排列整齐,枝晶间有尺寸为1.5~2.6μm的花瓣形γ′相析出。与700℃时试样的拉伸性能相比,950℃时抗拉强度降低了46.3%,而伸长率提高了200%,这说明高温拉伸强度降低,塑性增加。中温拉伸时,枝晶间长条形碳化物是断裂的主要裂纹源及扩展通道。而高温拉伸时,晶界处的碳化物、共晶成为裂纹源,裂纹沿晶界扩展,形成了沿晶断裂形貌。

粉末冶金TC11钛合金的热等静压制备与高周疲劳性能研究

粉末热等静压(HIP)技术可以近净成形高性能钛合金复杂构件,在航空航天领域具有广阔的应用前景。采用无坩埚感应熔炼超声气体雾化法制备了TC11预合金粉末,并对预合金粉末进行表征;在940℃/140 MPa/3 h条件下HIP成形了TC11坯体。采用OM、SEM、拉伸、冲击和旋转弯曲疲劳等手段对HIP坯体的显微组织和力学性能进行表征,研究了微气孔对HIP坯体疲劳性能的影响。结果表明,HIP坯体接近理论全致密,组织细小均匀,静力学性能接近甚至部分指标超越锻造合金,旋转弯曲高周疲劳强度(107周次)为590 MPa;空心粉形成的微气孔导致高周疲劳寿命呈现二重性,疲劳加载条件下,表面微气孔会优先成为裂纹萌生的位置,显著降低HIP坯体的高周疲劳寿命。