Additive manufacturing of metallic components – Process, structure and properties

Additive manufacturing of fatigue resistant materials: Challenges and opportunities

Effect of surface nanostructure on tensile behavior of superalloy IN718

Fatigue crack initiation in the direct aged version of the nickel-based superalloy Inconel 718 has been investigated at room temperature in the low stress/very high cycle regime via ultrasonic fatigue testing. Three different microstructures have been examined at the same strain amplitude in order to understand the influence of non-metallic inclusions (NMIs), i.e. carbides, carbonitrides and nitrides, and Σ3 twin boundary density on lifetime and failure mode. A slight refinement in grain structure and a higher Σ3 twin boundary density is associated with substantial reductions in lifetime. Decreasing Σ3 twin boundary density for fine grain microstructures results in a change in crack initiation mechanism from strain localization within grains at the high end of the grain size distribution to cracking of NMIs. To study the early stages of crack initiation and growth, specimens with pre-cracked NMIs were also tested in order to examine the role of the surrounding grain structure. Pre-cracked NMIs mainly result in macroscopic failure initiation at NMIs independent of the wrought microstructure. However, pre-loading specimens within the plastic domain highlighted the competition in crack initiation mode between cracked-NMIs and favorably oriented twin boundaries. Crack arrest from most of the pre-cracked NMIs demonstrates that surrounding grain structure (grain orientation, local plasticity and roughness in the vicinity of crack tip due to pre-straining) play a key role in the fatigue life of components stressed in the nominal elastic regime.

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Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Recent advances in the field of cold spray have put forward the potential of this deposition technique to be used as a non-thermal additive manufacturing process with significantly high deposition rates. In this study, we use the additive manufacturing potential of cold spray for fabrication of freestanding three-dimensional Inconel 718 samples, which is a challenging material for cold spray due to its high hardness and limited deformability. Additionally, we fabricated samples with similar geometry using one of the most common additive manufacturing methods, i.e. selective laser melting. Microstructural characteristics, distribution of residual stresses, porosity and structural integrity of the cold spray deposited samples were compared with those obtained by selective laser melting before and after different heat treatments. The results of the first time study of axial fatigue strength of cold spray deposited freeform samples indicate the notable efficiency of cold spray for fabrication of freestanding objects for structural components, with similar characteristics to those obtained from laser based additive manufacturing technique and even comparable to bulk material properties. The low working temperature of the cold spray method, suggests it as a promising additive manufacturing technique with a high potential to address many challenges regarding laser based approaches.

Cold spray deposition for additive manufacturing of freeform structural components compared to selective laser melting

Fatigue and fracture behavior of nickel-based superalloy Inconel 718 up to the very high cycle regime

基于镍的单个水晶 superalloy 与的低周期的疲劳(LCF ) 行为[001 ] 取向在 T0 掳 C 的中间的温度和 T0 + 的更高的温度被学习在 10 的经常的低紧张率下面的 250 掳 C ? 3 s ? 1 在周围的空气。superalloy 展出了依赖于温度并且使用紧张振幅的周期的紧张压缩不对称现象。破裂表面上的分析证明表面和表面下的扔 micropores 是主要裂缝开始地点。内部 Ta 富有的碳化物经常在所有标本被观察。骨折的二种不同类型被 frac-togaphy 建议。一种类型被模式描绘 -- 我与一台用显微镜裂开在 T0 + 的不平的表面 250 掳 C。而在更低的温度 T0C 的另外的类型赞成了中的一个或几八面 { 111 } 飞机，与正常模式相对照 -- 我生长模式典型地在低装载观察了频率(几 Hz ) 。为二个裂开的模式的失败机制纬鈥 ? 正在砍在 T0 + 在矩阵和纬 / 纬鈥 ? 接口在 T0 掳 C 和裂开的反对 ned 和矩阵猛抛 250 掳 C。

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Papers

Fatigue and fracture behavior of nickel-based superalloy Inconel 718 up to the very high cycle regime

Temperature effect on low-cycle fatigue behavior of nickel-based single crystalline superalloy