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

以金属粉末为基材生产的零件的最终密度是实现接近变形合金力学性能的关键。如果在工业环境中实现更高的密度，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，可以捕获更大量的高性能金属部件。本研究的主要目的是通过液相烧结的方法来开发母合金，以促进绿色钢坯的致密化和合金元素的最佳分布。有趣的是，与这一目标相关的挑战是传统粉末冶金（PM）和粘结剂喷射增材制造工艺的共同挑战。我们的项目旨在开发熔化温度低于PM钢典型烧结温度的主合金。烧结过程中形成的液相有几个目的：1)降低对氧有高亲和力的元素的化学活性，使它们对氧化不那么敏感；2)形成液相（5-8vol-%），使铁颗粒湿润，有利于它们在更密集的堆积中重排；3) Fe具有显著的溶解度，通过溶解-再沉淀过程促进质量传递，有利于颈部生长；4)液相烧结加速合金元素在钢基体内的空间分布；5)在残余孔隙周围，使其不易成为应力集中点、裂纹萌生/扩展点等。主合金将使用拉瓦尔大学粉末冶金实验室（lamoul）提供的水雾化器雾化。传统的PM部件以及AM粘合剂喷射样品将被压制/打印。研究将确定粒度分布、烧结剖面以及烧结气氛对成分和露点的影响。还将进行建模和控制维度变化作为上述变量的函数。最后，对最有前途的中间合金的拉伸性能和抗疲劳性能进行了量化。这里总结的研究与金属粉末工业联合会在其2017年PM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PM组件和2)金属AM。这里简要总结的工作将促进经济高效的高密度组件的发展，这些组件由机械性能与锻造相当的材料制造。此外，这些收益将通过可持续的制造工艺来实现，这些工艺被认为可以减少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.