Influence of Previous Particle Boundary on high-temperature strengths of PM superalloy

PPB（先前的颗粒边界）已知会降低粉末冶金合金的韧性和延展性。锻造工艺通常在通过HIP烧结后应用，以粉碎PPB，这是由粉末表面上的杂质引起的。等离子体旋转电极法（PREP）是一种能够减少难熔金属粉末中杂质的方法。在本研究中，为了减少PPBs，将PREP应用于合金718粉末。在δ-亚固溶线温度下对合金粉末进行热等静压处理，以获得超细晶粒和高强度。研究了PREP处理对粉末冶金718合金拉伸性能和显微组织的影响。PREP处理后，粉末中的杂质减少。发现PREP增加了烧结试样的密度。然而，由于PPB中的氧含量和细小沉淀物的减少不充分，它没有如预期那样改善延展性。

PPB (prior particle boundary) is known to decrease the toughness and ductility of PM alloys. The forging process is generally applied after sintering by HIP to crush PPBs, which are caused by impurities on the surface of the powder. The PREP(Plasma Rotating Electrode Process) is known to capable of reducing impurities in refractory-metals powder. In this study, to reduce PPBs, PREP was applied to alloy 718 powder. The alloy powder was HIPed at a delta-subsolvus temperature to achieve a superfine grain and high strength. The influence of PREP treatment on tensile properties and the microstructure of P/M 718 were investigated. After PREP treatment, the impurities in the powder were reduced. The PREP was found to increase the density of the sintered specimen. However, it did not improve ductility as expected due to an insufficient reduction of the oxygen content and fine precipitates in PPB.