The high deposition rate additive manufacture of nickel superalloys and metal matrix composites
The high deposition rate additive manufacture of nickel superalloys and metal matrix composites
复制标题
DOI：
--
复制
发表时间：
2016-05
期刊：
影响因子：
--
通讯作者：
D. Cooper
中科院分区：
文献类型：
--
作者：
D. Cooper
增材制造（AM）工艺的沉积速率是通过AM经济地生产金属材料的重要因素。如果整个技术，特别是镍合金要在工业中得到更广泛的采用，就必须实现更高的沉积速率。本论文研究了两种技术的潜力，高功率（> 1 kW）激光束在粉末床激光熔化（LM）配置和等离子体转移电弧焊（PTAW）使用送丝的方法沉积Inconel 625，广泛使用的镍高温合金。确定了在单焊缝和多层焊缝中稳定沉积材料所需的工艺参数，并对沉积材料进行了表征。进行了使用500μm层厚的高沉积速率粉末床LM，并表征了单个焊缝的工艺稳定性图。多层多焊缝样品实现了99.8%的可接受的相对材料密度，使用随着高度增加而降低的激光功率作为热控制策略以实现0.023cc/s的沉积速率，生产率比现有的低沉积速率粉末床LM（0.0036cc/s）增加了一个数量级。发现在500μm层处的沉积由于光束直径与层厚度的较低比率而赋予微观结构二次对准，因此传导冷却到相同层内的先前沉积的焊接轨迹中变得显著。研究了Inconel 625的PTAW沉积，并编制了表征平板实验单珠的工艺图。多层，多焊缝功能的沉积策略也进行了研究和热控制的重要性，由于从基板的热绝缘。PTAW沉积材料的特点是在高温下使用传统的拉伸试验和电阻加热的试样，使用Gleeble热机械模拟器，验证红外热成像的新用途，以测量热标距长度的拉伸试验。除了需要增加沉积速率之外，AM中关于镍合金的材料性能的限制目前受到与超合金相关的可焊性和开裂问题的限制。本论文研究了Inconel 625基金属基复合材料的生产潜力，这可能会对材料性能带来好处。确定了候选陶瓷增强材料，并进行了可行性研究，确定TiC为最有前途的候选材料。将原料粉末混合并评估，将TiC直接与Inconel 625混合，并将纯Ti和石墨形式的碳与Inconel 625混合，以研究原位反应加工路线。在100μm和500μm层厚下表征了两种MMC原料的工艺参数窗口，并使用预热来建立存在的关系。创建了工艺稳定性图，并且TiC的存在显著地影响了激光穿透粉末床的能力，这不是由于其高熔点，而是由于其高吸收率，这导致粉末床内的更大熔化，这阻碍了穿透和与基材的润湿。TiC的原位形成是部分成功的，但是由于在加工期间碳的均匀存在，形成了不需要的Mo 2C碳化物并且基体结构受到影响。激光束的功率密度被确定为决定基体内TiC的溶解和再沉淀行为的关键因素，而不是常用的能量密度度量。
The deposition rate of Additive Manufacture (AM) processes are a significant factor for the economic production of metallic materials by AM. Higher deposition rates must be achieved if the technology as a whole and nickel alloys in particular are to be more widely adopted within industry. This thesis investigates the potential of two techniques, high power (>1kW) laser beams within a powder bed laser melting (LM) configuration and Plasma Transferred Arc Welding (PTAW) using a wire fed approach for the deposition of Inconel 625, a widely used nickel superalloy. The processing parameters required for stable deposition of material in both single welds and multiple layers was determined, and the deposited material characterised. High deposition rate powder bed LM using 500μm layer thicknesses was conducted and a process stability map for single welds was characterised. Multi-layer multi-weld samples achieved an acceptable relative material density of 99.8%, using a reduction in laser power with increasing height as a thermal control strategy to achieve a deposition rate of 0.023cc/s, an order of magnitude increase in productivity over existing low deposition rate powder bed LM (0.0036cc/s). Deposition at 500μm layers was found to impart a secondary alignment to the microstructure due to a lower ratio of beam diameter vs. layer thickness, thus conductive cooling into previously deposited weld tracks within the same layer becomes significant. PTAW deposition of Inconel 625 was investigated and a process map characterising single bead on plate experiments has been compiled and presented. Deposition strategies for multi-layer, multi-weld features have also been investigated and the importance of thermal control due to thermal isolation from the substrate shown. PTAW deposited material has been characterised by tensile testing at elevated temperatures using both conventional tensile tests and by electrical resistance heating of specimens using a Gleeble thermo-mechanical simulator, validating the novel use of infra-red thermography to measure the thermal gauge length. In addition to a need for increased deposition rate, the limits of material performance in AM with respect to nickel alloys are currently constrained by superalloy related weldability and cracking problems. The work presented in this thesis examines the potential for production of an Inconel 625 based Metal Matrix Composite, which may offer benefits to material properties. Candidate ceramic reinforcement materials were identified and a feasibility study was conducted, identifying TiC as the most promising candidate. Feedstock powders were mixed and assessed, mixing TiC directly with Inconel 625 and mixing pure Ti and carbon in the form of graphite with Inconel 625 to investigate an in-situ reactive processing route. The process parameter windows were characterised for both MMC feedstocks at both 100μm and 500μm layer thickness and with the use of pre-heating to establish the relationships present. Process stability maps were created and significantly the presence of TiC affected the ability of the laser to penetrate the powder bed, not due to its high melting point, but due to its high absorptivity which results in greater melting within the powder bed which hinders penetration and wetting with the substrate. The in-situ forming of TiC was partially successful, but unwanted Mo2C carbides were formed and the matrix structure affected due to the homogenous presence of carbon during processing. The power density of the laser beam was identified as the critical factor in determining the dissolution and re-precipitation behaviour of TiC within the matrix, as opposed to the commonly used energy density metric.