Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes more severe in the fabrication of large-sized parts during the multi-laser L-PBF process. Therefore, investigations of spatter generation and countermeasures have become more urgent. Although much research has provided insights into the melt pool, microstructure, and mechanical property, reviews of spatter in L-PBF are still limited. This work reviews the literature on the in situ detection, generation, effects, and countermeasures of spatter in L-PBF. It is expected to pave the way towards a novel generation of highly efficient and intelligent L-PBF systems.

Selective laser melting (SLM) is the commonly term to describe the process in which a high energy laser beam scans the surface of a metal powder bed and the melted powder solidifies to form the bulk part [1] . SLM make it possible to create final function parts without post processing steps. Manufacturing businesses aiming to deliver their new products more quickly increasingly employ selective laser sintering/melting (SLS/SLM) for fabricating high quality, low cost, repeatable, and reliable alloy powdered parts for automotive, aerospace, and aircraft applications [2] . SLS can indirectly form integral control-shaped capsule for hot isostatic pressing (HIP) and mould core for casting, and SLM can directly and rapidly form HIP-shaped capsule [3] . SLM is complicated because of its high laser scan velocity and phase transformation in a sharply short time. Temperature field in this process is inhomogeneous [4][5][6] . Meanwhile, temperature evolution history would have significant Abstract: Selective laser melting (SLM) is a promising technique for additive manufacturing. During SLM of metallic powder, the temperature field and thermal history are important to understand physical phenomena involved. The purpose of this study is to simulate the temperature field during the SLM process of a hollow cylinder shape part based on a fully threaded tree (FTT) technique, and to analyze the temperature variation with time in different regions of the part. A revised model for temperature field simulation in the SLM process was employed, which includes the transition of powder-to-dense sub-model and a moving volumetric Gaussian distribution heat source sub-model. The FTT technique is then adopted as an adaptive mesh strategy in the simulation. The simulation result shows that during the SLM process of cylinder part, the temperature of inner powder bed is obviously higher than external one. The temperature at the internal of the molten pool is also higher than external, which may lead to differences in microstructures and other properties between the two regions.Key words: fully threaded tree; selective laser melting; temperature distribution; numerical simulation effects on final quality of parts. Large temperature gradients increase residual stresses and distortion and even lead to cracks in parts. Therefore, it is significant for SLM researchers to understand the mechanism of this process and effects of the parameters. Experiments regarding temperature fields, which greatly influence the formation of defects during the process, are lacking. It is a difficult work for most researchers to gain the detailed temperature field and its history during SLM process based on present experiment conditions. So, numerical simulation plays a significant role in the study of thermal behaviour during SLM process. The aim to perform temperature field simulation of SLM processes is to reduce the experimental cost, reveal the transient thermal history that cannot be obtained by limited experiment, and understand the evolution of microstructure...

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Hot isostatic pressing (HIP) and subsequent heat-treatments (HT) are necessary for titanium aluminide (TiAl) casting components. But there are few studies carefully comparing the microstructure changes from the initial as-cast condition to the final heat-treated condition. In this study, the microstructures of Ti-47Al-2Cr-2Nb (at%) alloy in the as-cast, as-HIPed and as-heat-treated conditions were characterized by optical microscopy and scanning electron microscopy. The mechanical properties after HTs were determined by the tensile tests at 700 °C. The results show that after HIP and HTs, all the microstructures exhibit a nearly lamellar (NL) structure and can be divided into an edge region and a central area. The microstructure after HIP in the edge region is normal, while distorted lamellae and many fine recrystallized grains exist in the central area. The yield strengths after three HTs are nearly the same, but the elongation after the HT at 1310 °C is much more than that after HTs at 1185 °C and 1280 °C. A refinement of colony size induced by distorted lamellae in as-HIPed condition is considered responsible for the great improvement in elongation.

In order to enhance smooth blasting adaptability and its effect in mining for rock mass complex characteristics, and based on the dynamic finite element analysis software with the material model of Mat-Plastic-Kinemetic, the dynamic stress characteristics and failure mechanism of blast-hole near-field with level soft interlayer are researched on different air-decked charge structures. The main effect of soft interlayer on top-air-decked charge structure is the tensile strength and range at the top of blasting hole, but the main effect of soft interlayer on middle-air-decked charge structure is the tensile strength and range at the middle of blasting hole, and some effect of soft interlayer on bottom-air-decked charge structure is the extension of rock crack at the bottom of blast- hole.