Effect of Initial Temperature on the Microstructure and Properties of Stellite-6/Inconel 718 Functional Gradient Materials Formed by Laser Metal Deposition

Stelite-6/Inconel 718 functionally gradient materials (FGM) is a heat-resisting functional gradient material with excellent strength performance under ultra-high temperatures (650–1100 °C) and, thus, has potential application in aeronautic and aerospace engineering such as engine turbine blade. To investigate the effect of initial temperature on the microstructure and properties of laser metal deposition (LMD) functional gradient material (FGM), this paper uses the LMD technique to form Stelite-6/Inconel 718 FGM at two different initial temperatures: room temperature and preheating (300 °C). Analysis of the internal residual stress distribution, elemental distribution, microstructure, tensile properties, and microhardness of 100% Stelite-6 to 100% Inconel 718 FGM formed at different initial temperatures in a 10% gradient. The experimental results prove that the high initial temperature effectively improves the uneven distribution of internal residual stresses. Preheating slows down the solidification time of the melt pool and facilitates the escape of gases and the homogeneous diffusion of elements in the melt pool. In addition, preheating reduces the bonding area between the gradient layers, enhancing the metallurgical bonding properties between the layers and improving the tensile properties. Compared with Stellite-6/Inconel 718 FGM formed at room temperature, the mean yield strength, mean tensile strength, and mean elongation of Stellite-6/Inconel 718 FGM formed at 300 °C are increased by 65.1 Mpa, 97 MPa, and 5.2%. However, the high initial temperature will affect the hardness of the material. The average hardness of Stellite-6/Inconel 718 FGM formed at 300 °C is 26.9 HV (Vickers hardness) lower than that of Stellite-6/Inconel 718 FGM formed at 20 °C.

Synthesis of a Novel Intumescent Flame Retardant Oligomer and its Application in ABS Copolymer

A novel intumescent flame retardant oligomer containing phosphorous-nitrogen structure (PSPTR) was synthesized and characterized by Fourier Transform Infrared (FTIR) and Mass Spectrometry (MS). The thermal behavior of PSPTR was investigated by thermogravimetric analysis (TGA). The TGA data shows that PSPTR has a high initial temperature of thermal degradation and a high char residue of 41.18wt% at 700 . A novel intumescent flame retardant (IFR) system, which is composed of PSPTR and novolac phenol (NP), was used to impart flame retardancy of ABS. The combustion behaviors of the ABS/IFR composites were investigated by Limiting Oxygen Index (LOI) and UL-94 tests. When the content of IFR (PSPTR:NP=1:1 mass ratio) is 30 wt%, the LOI value of ABS/IFR reaches 28.2, and the vertical burning test reaches UL-94 V-1 rating.