Three-dimensional simulation of sintering crunodes of metal powders or fibers by level set method

The difference of sintering crunodes of metal powders and fibers is discussed. The mathematical model of the surface diffusion described by the difference in mean curvature is defined as a Hamilton-Jacobi-type equation, and the model is numerically solved by the level set method. The three-dimensional numerical simulations of two metal powders and fibers(the fiber angle is 0° or 90°) are implemented by this mathematical model, respectively. The numerical simulation results accord with the experimental ones. The sintering neck growth trends of metal powders and metal fibers are similar. The sintering neck radius of metal fibers is larger than that of metal powders. The difference of the neck radius is caused by the difference of geometric structure which makes an important influence on the curvature affecting the migration rate of atoms.

Sintering behaviors of porous 316L stainless steel fiber felt

Isothermal sintering experiments were performed on the 316 L stainless steel fiber felts with fiber diameters of 8 μm and20 μm. Surface morphologies of the sintered specimens were investigated by using scanning electron microscopy(SEM) and optical microscopy. The results show that the amount of the sintering necks and the relative densities of the fiber felt increase with the increasing of both the sintering temperature and the sintering time. And the activation energies estimated present a decline at high relative densities for both 8 μm and 20 μm fiber felts. Moreover, the sintering densification of the fiber felts is dominated by volume diffusion mechanism at low temperature and relative densities. As more grain boundaries are formed at higher temperature and relative density, grain boundary diffusion will also contribute to the densification of the specimen.

A yttrium-containing high-temperature titanium alloy additively manufactured by selective electron beam melting

A yttrium-containing high-temperature titanium alloy(Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si-0.1Y, mass fraction, %) has been additively manufactured using selective electron beam melting(SEBM). The resulting microstructure and textures were studied using scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and electron backscattered diffraction(EBSD) and compared with the conventionally manufactured form. A notable distinct difference of microstructures is that additive manufacturing by SEBM enables homogeneous precipitation of fine Y2O3 dispersoids in the size range of 50-250 nm throughout the as-fabricated alloy, despite the presence of just trace levels of oxygen(7×10-4, mass fraction) and yttrium(10-3, mass fraction) in the alloy. In contrast, the conventionally manufactured alloy shows inhomogeneously distributed coarse Y2O3 precipitates, including cracked or debonded Y2O3 particles.

粉床电子束增材制造生物医用Ti-35Nb-5Ta-7Zr-xSi合金的性能研究

由不含毒性的合金元素组成的β钛合金具有低模量和优异的生物相容性,被认为是具有广泛应用前景的下一代生物医用材料。但强度和耐磨性的不足,限制了医用β钛合金在骨科临床上的应用。因此,本文在经典的β钛合金Ti-35Nb-5Ta-7Zr基础上,通过0~5 at%的硅元素添加,同时为了迎合临床医学对骨科植入材料定制化的发展趋势,采用粉床电子束增材制造技术进行高强、耐磨医用β钛合金的制备,并研究了硅元素的添加对合金微观组织、力学性能和摩擦磨损性能的影响规律。结果表明,硅的添加显著细化了合金的晶粒,大幅度提高了合金的强度,并且保持了相对较低的弹性模量。5 at%Si合金表现出了最优异的强度、弹性模量和耐磨性,有望作为临床应用的下一代骨科植入材料。