Laser Micro Sintering – A Quality Leap through Improvement of Powder Packing

Laser micro sintering, a modification of selective laser sintering for freeform fabrication of micro-parts, was continuously upgraded since its first application. Poor density of the powder layers has been a persisting problem that had to be dealt with from the beginning. One solution was the application of high intensity q-switched laser pulses. Compaction of the material and improvement of the sinter resolution was achieved. But with these pulse-regimes only limited density of the sintered body has been achievable. Recently special efforts have been made to get rid of or at least reduce these drawbacks by markedly higher compaction of the respective powder layers. There is clear evidence that with sufficiently compacted powder layers even laser micro sintering with continuous radiation should be feasible. Till recently laser sintering of metal had been applied mainly to produce monolithic components. With the upgraded technique direct generation of micro devices with freely movable subassemblies can be possible.Mechanical Engineerin

Masses of light tetraquarks and scalar mesons in the relativistic quark model

Masses of the ground state light tetraquarks are dynamically calculated in the framework of the relativistic diquark-antidiquark picture. The internal structure of the diquark is taken into account by calculating the form factor of the diquark-gluon interaction in terms of the overlap integral of the diquark wave functions. It is found that scalar mesons with masses below 1 GeV: f_0(600) (\sigma), K^*_0(800) (\kappa), f_0(980) and a_0(980) agree well with the light tetraquark interpretation.Comment: 9 pages, Report-no adde

Electronic structure and x-ray magnetic dichroism in random substitutional alloys of f-electron elements

The Koringa-Kohn-Rostoker —coherent-potential-approximation method combines multiple-scattering theory and the coherent-potential approximation to calculate the electronic structure of random substitutional alloys of transition metals. In this paper we describe the generalization of this theory to describe f-electron alloys. The theory is illustrated with a calculation of the electronic structure and magnetic dichroism curves for a random substitutional alloy containing rare-earth or actinide elements from first principles

Processing of Silicon Carbide by Laser Micro Sintering

Silicon carbide – a solid with covalent bonds - is conventionally synthesized via the Acheson process. Usually solid bodies of silicon carbide with definite shapes are generated from the grained material via hot isostatic pressing or liquid phase sintering. Both processes are conducted under well-controlled temperature regimes. Applying the freeform fabrication technique “Laser Micro Sintering” poses a big challenge to experimental skill due to the nonequilibrium conditions that are characteristic features of laser material processing. Successive layers SiC layers with a thickness of 1μm were processed with coherent radiation of 1064 nm. The specific behavior of two different silicon carbide powders - one of them blended with additives - are reported along with interpretational approaches.Mechanical Engineerin

Interpretation of x-ray-absorption dichroism experiments

A rule is derived to use x-ray magnetic circular dichroism spectra to extract the magnetic moment of the conduction-band states with j= l -1/2 separately from those with j= l + 1/2 as a function of energy. This quantity is straightforward to determine from the electronic band structure. The rule is illustrated with an application to pure iron and to the random substitutional alloy Fe_{80}CO_{20}

Effect of chemical disorder on NiMnSb investigated by Appearance Potential Spectroscopy: a theoretical study

The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with unique properties for future applications. Band structure calculations predict exclusively majority bands at the Fermi level, thus indicating {100%} spin polarization there. As one thinks about applications and the design of functional materials, the influence of chemical disorder in these materials must be considered. The magnetization, spin polarization, and electronic structure are expected to be sensitive to structural and stoichiometric changes. In this contribution, we report on an investigation of the spin-dependent electronic structure of NiMnSb. We studied the influence of chemical disorder on the unoccupied electronic density of states by use of the ab-initio Coherent Potential Approximation method. The theoretical analysis is discussed along with corresponding spin-resolved Appearance Potential Spectroscopy measurements. Our theoretical approach describes the spectra as the fully-relativistic self-convolution of the matrix-element weighted, orbitally resolved density of states.Comment: JPD submitte

Rare radiative B decays to orbitally excited K mesons

The exclusive rare radiative B meson decays to orbitally excited axial-vector mesons K_1^*(1270), K_1(1400) and to the tensor meson K_2^*(1430) are investigated in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. These decays are considered without employing the heavy quark expansion for the s quark. Instead the s quark is treated to be light and the expansion in inverse powers of the large recoil momentum of the final K^{**} meson is used to simplify calculations. It is found that the ratio of the branching fractions of rare radiative B decays to axial vector K^*_1(1270) and K_1(1400) mesons is significantly influenced by relativistic effects. The obtained results for B decays to the tensor meson K_2^*(1430) agree with recent experimental data from CLEO.Comment: 17 pages, revte

Industrial Freeform Generation of Microtools by Laser Micro Sintering

Precision tools with structural resolution reaching the 20 micrometer range can be generated on an industrial scale by “laser micro sintering”. Components featuring aspect ratios above 12 and a roughness Ra down to 1.5 micrometers have already been produced from sub micrometer grained metal powders. The components can be generated either firmly attached to a substrate or fixed in an easily separable mode. If supporting structures are employed, undercuts up to 90° are feasible, without, a process parameter dependent maximum angles of undercut below 90° are obtained. The process has been introduced into the market, labeled microSINTERING by 3D-Micromac AG.Mechanical Engineerin