Development of master alloys for improving the sintering response and mechanical properties of high performance steel components produced by powder metallurgy and additive manufacturing

用金属粉末作为基础材料生产的部件的最终密度是实现接近锻造合金的机械性能的关键。如果在工业背景下可以实现更高的密度，低成本和更可持续的生产工艺，如粉末冶金或粘合剂喷射增材制造，可以捕获更大体积的高性能金属部件。本研究的主要目的是开发中间合金，以促进致密化的绿色钢压坯和合金元素的最佳分布，通过基于液相烧结的方法。有趣的是，与这一目标相关的挑战是传统粉末冶金（PM）和粘合剂喷射增材制造工艺所共有的。我们的项目旨在开发熔化温度低于粉末冶金钢典型烧结温度的中间合金。在烧结过程中形成的液相将用于几个目的：1）降低对氧具有高亲和力的元素的化学活性，使它们对氧化不太敏感; 2）形成液相（5-8vol-%），其将润湿铁颗粒，有利于它们以更致密的堆叠重新排列; 3）对Fe显示出显著的溶解度，以通过溶解-再沉淀过程改善质量传递并有利于颈部生长; 4）通过液相烧结加速合金元素在钢基体内的空间分布; 5）使残余孔隙变圆，使其不易于充当应力集中器、裂纹起始/扩展位点，母合金将使用拉瓦尔大学粉末冶金实验室（LAMPOUL）提供的水雾化器进行雾化。将对常规PM部件以及AM粘合剂喷射样本进行压制/打印。将进行研究以确定粒度分布、烧结曲线以及烧结气氛对成分和露点的影响。还将开展工作，根据上述变量对尺寸变化进行建模和控制。最后，最有前途的中间合金的拉伸性能以及抗疲劳性能将被量化。这里总结的研究与金属粉末工业联合会在其2017年粉末冶金行业路线图中确定的4个主要主题中的2个直接相关，即：1）高密度粉末冶金部件和2）金属AM。本文简要总结的工作将促进开发具有成本效益的高密度部件，这些部件由机械性能与锻造材料相当的材料制成。此外，这些收益将通过使用可持续的制造工艺来实现，这些工艺被认为可以降低能源消耗和生产成本。

Final density of components produced with metal powders as base material is key to achieve mechanical properties approaching those of wrought alloys. Should higher densities become reachable in an industrial context, low-cost and more sustainable production processes such as powder metallurgy or binder-jetting additive manufacturing could capture a larger volume of high-performance metallic components. The main objective of this research is to develop master alloys to promote densification of green steel compacts and optimum distribution of alloying elements through an approach based on liquid phase sintering. Interestingly, the challenges related to this objective are common to conventional powder metallurgy (PM) and binder-jetting additive manufacturing processes. Our project aims at developing master alloys with a melting temperature lower than the typical sintering temperature used for PM steels. The liquid phase that will form during sintering will serve several purposes: 1) Reduce the chemical activity of elements with high affinity for oxygen making them less sensitive to oxidation; 2) Form a liquid phase (5-8vol-%) that will wet the iron particles favouring their rearrangement in a denser stacking; 3) Show significant solubility for Fe to improve mass transport and favour neck growth through a process of dissolution-reprecipitation; 4) Accelerate spatial distribution of alloying elements within the steel matrix through liquid phase sintering; 5) Round the residual pores making them less susceptible to act as stress concentrators, crack initiation/propagation sites, etc. The master alloys will be atomized using the water atomizer available at the Powder Metallurgy Laboratory of Université Laval (LAMPOUL). Conventional PM parts as well as AM binder-jetted specimens will be pressed/printed. Studies will be carried out to determine the influence of particle size distribution, sintering profile as well as sintering atmosphere in terms of composition and dew point. Work will also be performed to model and control dimensional change as a function of the variables identified above. Finally, tensile properties as well as fatigue resistance of the most promising master alloys will be quantified. The research summarized here is directly related to 2 of the 4 main topics identified by the Metal Powder Industries Federation in its 2017 PM Industry Roadmap, namely: 1) High-density PM components and 2) Metal AM. The work briefly summarized here will foster the development of cost-effective high-density components manufactured from materials with mechanical properties comparable to wrought. Moreover, these gains will be achieved using sustainable manufacturing processes that are recognized for reducing energy consumption and production costs.