Optimizing the Hot Isostatic Pressing Process

A genetic algorithm (GA) is used to optimize the hot isostatic pressing (HIPing) process for beryllium powder. The GA evaluates a HIPing model with different processing schedules in an effort to minimize temperature, pressure, processing time, ramp rates, grain growth, and distance to target relative density. It is shown that this is a constrained, multiobjective, noisy, optimization problem to which the GA is able to evolve a large number of viable solutions. However, for the GA to work in such a large multidimensional search space, it is suggested that the constraints be treated as objectives and then penalize the Pareto ranking for each constraint violated. This approach is necessary because a large-dimensional objective space naturally results in most members being Pareto rank 1.     

Surface Cracking of Ferrites in Hot Isostatic Pressing

1.IntroductionIn recent ten years full density ceramicshas been developed to meet the needs inelectronic industry and other applications.HIP process offers a more convenient wayto prepare high density materials[1—5].The fully densified ferrites have beenused as digital magnetic head.If the densityafter sintering is high enough,it could be     

含镁铝尖晶石的铝酸钙水泥的合成与流变特性

在1400℃和1500℃温度下合成了不同配比的铝酸钙水泥(CMA)。检测结果显示, 当温度升高时镁铝尖晶石的粒径由5 μm生长到15 μm。合成温度达到1400℃时, 镁铝尖晶石晶粒呈团簇状并分布在铝酸钙晶粒周围; 当合成温度升高至1500℃时, 镁铝尖晶石晶粒穿插在铝酸钙晶粒中。另外, 随着水泥中镁铝尖晶石含量的增加, 水泥的凝结时间延长, 同时粘度下降。相应的, 水泥储能模量和流动点的大小分别为0.15 MPa和4.44%。提高镁铝尖晶石相的含量或增大铝酸钙晶粒尺寸会减弱水泥水化时絮凝结构的强度。     

热等静压在铸造高温合金领域的应用

采用适当热等静压工艺处理铸造高温合金,利用高温高压实现铸件内部疏松孔洞的蠕变扩散,达到闭合疏松和均匀合金组织的目的,使铸造高温合金的综合力学性能,尤其是疲劳性能、塑性及合金力学性能的稳定性显著提高,大大提高了铸件使用的安全性和可靠性.介绍了热等静压工艺处理高温合金铸件的致密化原理、工艺因素及其对合金组织和性能的影响,同时概述了热等静压技术的应用成果及发展状况.     

镍基铸造高温合金热等静压处理的研究

就热等静压处理对镍基铸造高温合金的缺陷消除、组织和力学性能的改善作了研究。研究结果表明，通过热等静压处理后的合金，不仅可有效地消除合金中的缺陷（疏松和气孔），获得致密的合金，而且还可改善合金的显微组织，提高合金的持久、拉伸和疲劳性能，显著地减小性能分散度。     

Hot Isostatic Pressing. Heißisostatisches Pressen

Hot Isostatic Pressing (HIP) is a technique for producing structural parts under temperatures and pressures in a special sort of a sintering process. HIP is on one hand a forming technique, on the other hand a densifying technique HIP can also be used for diffusion welding especially for metal and ceramic composites.     

碳化硅和氧化铝陶瓷的热等静压氮化

通过对无压烧结、热压烧结和热等静压烧结ＳＩＣ陶瓷以及热压烧结的ＳｉＣ粒子补强Ａｌ２Ｏ３基复相陶瓷（ＳｉＣｐ－Ａｌ２Ｏ３）和ＳｉＣ粒子与ＳｉＣ晶须共同增强的Ａｌ２Ｏ３基复合材料（ＳｉＣｐ－ＳｉＣｗ－Ａｌ２Ｏ３）在氮气氛中进行高温氮化处理，成功地实现了这些材料的开口气孔表面裂纹的愈合。研究表明：热等静压氯化工艺可以显著提高ＳｉＣ和Ａｌ２Ｏ３陶瓷的抗弯强度，对断裂韧性也有较大的改善作用。对于热等静压烧结ＳｉＣ陶瓷，在１８５０℃和２００ＭＰａ氮气压力下氯化处理１小时后，其抗弯强度和断裂韧性分别由５８２ＭＰａ和５．７ＭＰａ·ｍ１／２提高到９０７ＭＰａ和８．４ＭＰａ·ｍ１／２；对于热压烧结的ＳｉＣｐ－Ａｌ２Ｏ３复相陶瓷和ＳｉＣｐ－ＳｉＣｗ－Ａｌ２Ｏ３复合材料，在１７００℃和１５０ＭＰａ氮气压力下氮化处理１小时后，其室温抗弯强度分别由４６０和７０５ＭＰａ提高到８９５和１０３３ＭＰａ。     

热等静压工艺在工程陶瓷领域中的应用与发展

热等静压（ＨＩＰ）是一种先进的陶瓷致密化工艺、本文简要介绍了ＨＩＰ设备，着重综述了ＨＩＰ工艺在工程陶瓷应用中所取得的研究最后概括敢ＨＩＰ工艺及设备的最新进展。     

Mechanisms of Polycrystalline CVD ZnS Densification during Hot Isostatic Pressing

The densification kinetics of CVD ZnS are studied during hot isostatic pressing by monitoring the porosity of the material. The process is shown to be accompanied by significant microstructural changes. The results indicate that, during hot isostatic pressing, both the diffusional coalescence and plastic deformation mechanisms are operative.     

AlN-BN复相陶瓷的热等静压制备与性能研究

以氮化铝(AlN)和氮化硼(BN)为原料, 无烧结助剂、热等静压烧结制备了AlN-BN复相陶瓷, 研究了热等静压温度和压强对两种不同原料配比(摩尔比)烧结试样的微观结构和性能的影响。结果表明: 增加BN的添加量对复相陶瓷的烧结致密化影响较小, 但逐渐降低硬度和热导率、增大体积电阻率。相同原料配比下, 复相陶瓷的密度越高, 其热导率、体积电阻率、硬度越高。热导率和体积电阻率的实测值与两相复合模型方程较为符合。当n_AlN:n_BN=75:25时, 在温度为1600℃、压强为90 MPa、保温3 h的热等静压工艺下可以制备出相对密度达98.03%、热导率为77.29 W/(m·K)、体积电阻率为1.35×10¹⁵ Ω·cm的复相陶瓷。     

Effect of Phase Transformation on Densification During Hot Isostatic Pressing

Densification of mixed phases which undergo phase transformation at elevated temperatures during hot isostatic pressing is described. The effect of the phase transformation on the densification process is shown relative to the densification characteristics of the major phase component of the mixed system. The densification of a mixed phase system undergoing phase transformation is compared using the mechanism maps for hot isostatic pressing of the single phase material. Densification of mixed phase systems undergoing phase transformation, such as homogenization with Kirkendall Effect, is considerably slower than its constituent single phase material. The tendency to generate Kirkendall pores due to homogenization of chemically different materials opposes the normal densification process, thus slowing down the densification process.     

Hot Isostatic Pressing of Plasma Sprayed Thermal Barrier Coating Systems

Thermal barrier coatings (TBC) are important to aerospace and high performance gas turbine engines because they help to keep the temperature experienced by the base metal low; thus, prolonging the life span of the material. Plasma spraying is a technique commonly used to deposit the ceramic-based TBC. An intermediate layer is applied to enhance the bond between the substrate and the ceramic top coat. However, the oxidation of the bond coat due to the infiltration of gas through the porous ceramic layer is a major problem encountered in TBC. This in turn leads to spalling and eventual destruction of the whole coating system. Hot isostatic pressing (HIP) was performed on a number of plasma sprayed thermal barrier coating systems to investigate the effects the process has on micro structure and other physical properties. Due to the fact that the majority of TBC is exposed to thermal cycling and thermal fatigue, it is hoped that the changes brought about by HIP in the porosity and microstructure will improve the life span and performance of TBC. HIP was performed in the temperature range 750-1300° C and pressures of 50-200 MPa. The bond coats that were studied include Ni-5% Al, Ni-20 percnt; Al, NiCrAl and NiCrAlY, while the ceramic coat was Zr0₂-5 wt percnt; CaO. Characterization of the coatings was carried out using scanning electron microscopy (SEM) and image analyser. The results showed the porosity of the coatings to be dramatically reduced to near zero levels. In addition, the other physical properties like hardness and Young's modulus increased over a wide temperature range.     

热等静压工艺参数对ZTC4钛合金力学性能的影响

为了使ZTC4钛合金铸件具有较优的力学性能,系统地研究了热等静压温度、时间、压力等工艺参数对ZTC4钛合金铸板力学性能的影响.结果表明:热等静压工艺参数变化对ZTC4钛合金室温拉伸性能、弯曲性能都有影响,其中对ZTC4钛合金伸长率的影响最为明显,但对冲击性能影响不显著.综合考虑各因素,在920℃/125MPa/2h热等...     

镁铝尖晶石超微粉的制备方法

主要介绍了国外近年来制备MgAl_2O_4超微粉的各种方法、特点,并比较了它们的优缺点,根据合成原理将制备方法分为二大类:液相法和固相法。     

Fracture of single crystal MgAl2O4

The fracture of single crystal, stoichiometric MgAl₂O₄ spinel, was investigated for the (1 0 0), (1 1 0), and (1 1 1) from room temperature to 1500° C. Two regions of fracture behaviour were observed; a low temperature elastic region where K _lc decreased with increasing temperature, and an elevated temperature region where K _lc increased rapidly with increasing temperature. The elastic region is explained primarily by the decrease of elastic modulus with increasing temperature, whereas the rapid increase of K _lc at elevated temperature is attributed to plastic flow in the vicinity of the crack tip     

MgO·1.5Al2O3透明陶瓷的无压/热等静压烧结制备

镁铝尖晶石透明陶瓷是典型的结构功能一体化材料, 具有优异的光学和机械性能。实验合成了颗粒细小、均匀的单相MgO·1.5Al₂O₃陶瓷粉末, 并且利用XRD全谱拟合软件Fullprof和尖晶石位置分配程序SIDR两步法确定其晶体结构为(Mg_0.46Al_0.54)^IV[Mg_0.26Al_1.64□_0.09]^VIO₄。再通过真空无压烧结结合热等静压烧结制备出了高性能的透明陶瓷, 热等静压18 MPa下1850℃烧结4 h所得样品的致密度达到99.75%, 厚度为2 mm的烧结样品可见光透过率达到65%, 红外波段透过率达到80%以上, 维氏硬度为(12.75±0.12) GPa, 杨氏模量为277 GPa。     

Hot Isostatic Pressing Modifications of Pore Size Distribution in Plasma Sprayed Coatings

Plasma sprayed coatings contain relatively large amount of pores. This is primarily due to the nature of deposition by the liquid droplets upon impact. This paper reports the modifications made in the pore size distribution of plasma sprayed yttria stabilized zirconia (YSZ) and Ti-6Al-4V/hydroxyapatite (HA) composite coatings following hot isostatic pressing (HIP). The pore size distribution was measured by a mercury intrusion porosimeter (MIP). The results indicated that the YSZ coatings which were HIPed for 1 hour and 3 hours in the temperature range 1000^° to 1200^°C and ∼185 MPa showed a small decrease in the average porosity (∼2.5%) for the 1 hour samples. However, the hardness increased ∼39%, and there was a corresponding increase in the coating density. This was due to reduction of the average pore size in the HIPed coatings. Thus, in the YSZ coatings, the pores responded to HIP by a general breakdown of large pores to smaller ones and effectively forming many 'new' interparticle contacts. Whilst the overall porosity was reduced marginally, the increase in physical property like hardness was significant because of the increase in interparticle and inter-lamellae contacts following HIP treatment. In the Ti-6A1-4V/HA composite coatings, the reduction of pores is most significant amongst the small pores. The porosity of the as sprayed 20 wt% HA composite was ∼19%. This value was reduced to 17% for the sample HIPed at 1,000%C for 1 hour. Although the reduction was relatively minor, the interesting aspect was the drastic reduction of small pores less than 0.3 μm. The average pore diameter was observed to increase from 0.1676 μm in the as sprayed coating to 0.787 μm in the sample HIPed at 1,000^°C, as a result of the elimination of the micro-pores. Physical properties such as microhardness, Young's modulus and density increased substantially. This is believed to be aided mainly by the plastic deformation of the ductile Ti-6A1-4V phase during HIP. Thus modification of the pore size distribution or even average pore size can elicit substantial improvement in the properties in two different material coating, albeit the difference in the manner the modification occur.     

MgAl2O4尖晶石涂层的显微结构

解XRD红外吸收光谱、ＴＥＭ和ＥＤＳ等方法研究了等离子喷涂尖晶石涂层的显微结构，结果表明，用等离子喷涂能获得结晶良好、阳离子分布比较有序的尖晶石涂层，涂层中尖晶石晶粒细小、均匀涂层热稳定性非常好，可在高温下长时间使用杂质可能导致涂层局部形成玻璃相涂层中尖晶石晶粒内存在大量位错，可能是在喷涂沉积过程中产生的变形所致