Microstructure Evolution of EBM Gamma Titanium Alumiide (TNM-B1)

在过去的十年中，增材制造已经成为科学和工业界的一大兴趣。这使得定制的组件制造能够广泛应用，例如在航空航天和医药行业。这些行业通常依赖于难以加工的材料。基于粉末床的方法，如电子束熔化工艺（EBM），因其工艺温度高、冷却速度慢而成为此类应用的最佳选择。Titan铝化物因其优异的高温性能和低密度而被认为是航空航天工业材料替代品的潜在候选者。然而，这些材料在约700 °C下表现出延性到脆性的转变。因此，通过选择性激光熔化（SLM）进行的铸造或加工（也是一种生成过程）容易受到热诱导裂纹的影响。EBM过程可以建立作为一个替代的加工路线，为近净形制造的复杂零件组成的这些material.This项目的重点是EBM制造的TNM-B1零件的微观结构演变的实验研究-TNM合金的进一步发展-沿着一个共同的EBM制造链。TNM合金是钛铝化物，与传统的γ-TiAl合金相比，由于减少了偏析和织构敏感性，因此具有改善的可加工性。TNM合金的微观结构显著影响部件性能，并通过EBM处理后的热处理进行控制。因此，本计画的重点是研究这两种制程对TNM合金组织演化的影响。因此，应处理两个主要方面。首先，元素可能蒸发，导致化学和相组成的变化，其次，与铸造的TNM-B1部件相比，可能发生微观结构变化。以往的研究已经强调了其他钛铝化合物在EBM加工过程中铝的蒸发。对于TNM系统，这可能导致脆性α 2-TiAl相的量增加，从而影响微观结构和残余应力状态。其结果可能是热致开裂的风险增加，尤其是在淬火步骤期间（例如，固溶退火热处理之后）。考虑到这一点，应研究残余应力沿着EBM制造链的演变和稳定性。残余应力检测的重点将放在EBM工艺之后的多步热处理上。根据所有结果，将评估EBM工艺在TNM-B1或TNM合金部件制造中的适用性。微观结构和残余应力状态调查的结果也将用于识别沿着EBM制造链的相关和关键工艺和工艺参数。

Over the past decade additive manufacturing has become of great scientific and industrial interest. This enables tailored component manufacturing for a wide range of applications, for example in aerospace and medicine industry. These industries often rely on difficult to process materials. Powder-bed based methods like the electron beam melting process (EBM) emerged as an excellent choice for such use cases due to high process temperatures and slow cooling rates.Titan aluminides are known to be a potential candidate for material substitution in aerospace industry due to their excellent high temperature behavior as well as low density. However these materials exhibit a ductile-to-brittle transition at around 700 °C. Thus casting or processing by selective laser melting (SLM), a generative process as well, are susceptible to thermal induced cracks. The EBM process could establish as an alternative processing route for near net shape manufacturing of complex parts consisting of those materials.This project focusses on the experimental investigation of the microstructural evolution of EBM-manufactured TNM-B1 parts – a further development of TNM-alloy – along a common EBM manufacturing chain. TNM alloys are titanium aluminides with improved workability due to decreased segregation and texture susceptibility compared to conventional gamma-TiAl alloys. The microstructure of TNM-alloys significantly influences the component properties and is controlled by a thermal treatment subsequent to the EBM-processing. Thus a key point of this project is to investigate the influence of those two processes on the microstructural evolution of TNM alloys. Thereby two main aspects shall be addressed. First a possible evaporation of elements which lead to changes of the chemical and phase composition and second a possible microstructural change in comparison to casted TNM-B1 components. Former researches already highlighted the evaporation of aluminum during EBM-processing for other titanium aluminides. For the TNM system this could lead to an increased amount of brittle alpha2-TiAl-phase and thus influence microstructure and residual stress state. An increased risk of thermal induced cracking especially during quenching steps (e.g. subsequent to the solution annealing heat treatment) might be the consequence. Taking this into account the evolution as well as the stability of residual stresses along the EBM-manufacturing chain shall be investigated. The emphasis of the residual stress examinations will be on the multi-step heat treatment subsequent to the EBM-process.Based on all results the applicability of the EBM-process for component manufacturing from TNM-B1 or TNM-alloys will be evaluated. There the outcomes of the microstructural and residual stress state investigations will also be used to identify relevant and critical processes and process parameters along the EBM manufacturing chain.