Microstructure and tensile property of SLM 316L stainless steel manufactured with fine and coarse powder mixtures

Selective laser melting(SLM)technology is the prevailing method of manufacturing components with complex geometries.However,the cost of the additive manufacturing(AM)fine powder is relatively high,which significantly limits the development of the SLM.In this study,the 316L fine powder and coarse powder with a mass ratio of 80:20,70:30 and 60:40 were mixed using a ball milling and the samples with a relative density greater than 97%were prepared by SLM.The results show that the intricate temperature gradients and surface tension gradients in SLM will produce Marangoni flow,forming a typical molten pool morphology,cellular and strip subgrain structures.And as the proportion of coarse powder increases,the scanning track morphology changes from smooth to undulating;the morphology of the molten pool and subgrain structure are weakened.Meanwhile,the unmelted particles appear on the surface of the SLM sample.On the premise of an introducing appropriate amount of large particle size powder(20%),the SLM samples still have good mechanical properties(662 MPa,47%).

Densification Mechanism of Warm Compaction and Powder Mixture Designing Rules

By phenomenological analysis of warm compaction, it is found that, compared with the contribution of particle plastical deformation to densification of powder compact,the particle rearrangement is a dominant densification mechanism for powder warm compaction, and the plastical deformation of particles plays an important role in offering accommodating deformation for particle rearrangement and densifying powder compact at the final stage of pressing.In order to attain density gain as high as possible during warm compaction, six rules for designing warm compacting powder mixtures were proposed in detail.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅰ: Phase Composition and Microstructure of Main Phase

It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of grains has its own domain and dislocation structure. There are mono- and polydomains with and without dislocations. The grains of the main phase of monoand polydomains without dislocations and polydomains with dislocations were formed by diffusion in the solid phase. In these conditions NiAl3 phase is located on the grain boundary of the main phase. The Ni2Al3 phase is located at the triple joints of the main phase.

Effect of mechanical activation on TiC synthesis reaction in Al-Ti-C powder mixture

After milling in a high energy ball miller for various times, the synthesis reaction process of the Al Ti C powder mixture were investigated by difference thermal analysis (DTA) and X ray diffractometry (XRD). According to the patterns of reaction peaks on the DTA curves, the activation energy of each reaction was calculated. The experimental results of DTA show that the synthesis reaction of Al Ti C powder mixture can be enhanced after high energy milling. The longer the milling time, the lower the reaction temperature. The synthesis reaction of TiC is transformed from Ti+C→TiC to Al 3Ti+C→TiC+3Al with long period milling. Meanwhile, the activation energy of the reaction reduces with increasing milling time. The effect of milling time on reduced activation energy for low temperature region is more significant than that for high temperature region.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅱ: Influence of Alloying by Boron on the Phase Composition and the Microstructure of Grains of the Main Phase

The Ni_3B phase was formed when boron (0.5 at. pct B) was added to the intermetallic of sto- ichiometric and off-stoichiometric (Ni-24 at. pct Al) compounds. In the alloy of stoichiometric composition the particles of Ni_3B phase has the size around 0.1μm and is located on the grain boundary of the main phase. The decreasing of concentrations of Al in the ofF-stoichiometric alloy leads to increase in the degree of the long-range order parameter, increasing the concen- trations of boron in the solid solution and decreasing its localization on the grain boundary. Microalloying of boron leads to increasing in the fraction of grain monodomains with disloca- tions up to 0.7 in the alloy of the off-stoichiometric composition and up to 1 in the alloy of the stoichiometric composition. It was established the correlation between the degree of the concentration inhomogeneity, average density of the dislocations and the average long range-order parameter.

Theoretical and experimental study on Compton scattering of a binary powder mixture

The relationship between Compton scattered photon counts per unit mass and the content of a component in a binary powder mixture is deduced based on the Compton scattering theory.This relationship can be regarded linear after some approximations.The scattered photon counts per unit mass increases faster with the content when the difference of the atomic numbers of the two components in the binary powder mixture is larger.The relationship was verified with Compton scattering experiments on a series of Ni-Cu and Fe-C binary powder mixtures.The method of using this linear dependene of scattered photon counts on the content of a binary powder mixture to ascertain the component content in a binary mixture was introduced.

Microstructural Evolution During Self-propagating High-temperature Synthesis of Ti-Al System

In order to investigate the microstructural evolution during self-propagating high-temperature synthesis （SHS） of Ti-Al powder mixture with an atomic ratio of Ti： Al=1：1, a combustion front quenching method （CFQM） was used for extinguishing the propagating combustion wave, and the microstructures on the quenched sample were observed with scanning electron microscope （SEM） and analyzed with energy dispersive spectrometry （EDS）. In addition, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction （XRD）. The results showed that the combustion reaction started from melting of the Al particles, and the melting resulted in dissolving of the Ti particles and forming of Al3Ti grains. As the Al liquid was depleted, the combustion reaction proceeded through solid-state diffusion between the solid Al3Ti and the solid Ti. This led to the forming of TiAl and Ti3Al diffusing layers. In addition, the combustion reaction is incomplete besides TiAl, there are a large amount of Ti3Al and TiAl3 and a small amount of Ti in the final product. This incompleteness chiefly results from the using of coarser Ti powder.

Study on the Protective Effect of the Mixture of Shengmai Powder and Danshen Decoction(生脉散丹参饮合剂)on the Myocardium of Diabetic Cardiomyopathy in the Rat Model

Objective：To study the protective effect of the Mixture of Shengmai Powder and Danshen Decoction（生脉散丹参饮合剂,abbreviated as the Mixture） in the rat model with type 2 diabetic cardiomyopathy （DCM）.Methods：Forty-two SD rats with DCM model,established by the combination of insulin resistance by a high-fat diet with the damage of pancreatic islet p cells by intraperitoneal injection of high dose streptozotocin （50 mg/kg） once,were evaluated in the damage of the myocardium by electrocardiogram at the end of 12 weeks of grouping and intervention administration;the extent of damage in the myocardial subcellular structure was observed by electron microscopy;the content of myocardial collagen in the left cardiac ventricle was quantified by Masson staining test;the myocardial cell apoptosis was determined by TUNEL;the changes in the mRNA expression levels of thrombospodin-1（TSP-1） and tribbles homolog 3（TRB-3） by real-time quantitative PCR,the expression levels of myocardial TSP-1,tumor growth factorβ1（TGF-β1）,TRB-3,and chymase were detected by immunohistochemistry,and the changes in the expression levels of myocardial TSP-1,active-TGF-β1 （A-TGF-β1） and latent-TGF-β1（L-TGF-β1） protein were tested by Western blotting.Results：Compared with the control group,the myocardial tissue was less damaged,and the extent of damage in the myocardial subcellular structure was less;the collagen fiber content and the cell apoptosis were reduced;the expression levels of TSP-1 mRNA and TRB-3 mRNA,the expression levels of myocardial TSP-1,TGF-β1,TRB-3,and chymase,as well as the average expression levels of the myocardial TSP-1,A-TGFβ1,and L-TGF-β1 protein were decreased in the Mixture group.Conclusion：The Mixture of Shengmai Powder and Danshen Decoction could inhibit the process of myocardial fibrosis in the rat myocardium of DCM through multiple pathways and significantly delay the genesis and progress of DCM in hyperglycemic rats.