Junji Kihara

Reaction synthesis of refractory disilicides by mechanical alloying and shock reactive synthesis techniques

Abstract The reaction synthesis of disilicides of Group IVA–VIA transition metals by mechanical alloying and shock reactive synthesis techniques has been investigated. All nine disilicide compounds were directly produced from their elemental powder mixtures by mechanical alloying. Moreover, the formation of some disilicides, such as MoSi 2 and NbSi 2 , proceeded by mechanically induced self-propagating reactions, the mechanism of which is analogous to that of the self-propagating high-temperature synthesis (SHS). Shock reactive synthesis of MoSi 2 , NbSi 2 , and TiSi 2 was conducted with a one-stage gun. Powder samples used for the shock study were prepared from metal–silicon powder mixtures that had been subjected to high-energy ball milling. The explosive driven flyer plate struck the sample-containing capsule at a velocity of 1 km s −1 . In most cases, shock-induced reactions went to completion. The effect of thermochemical driving force on the reactive formation of the disilicide compounds is discussed.

Magnetic powder forming simulation subjected to pressing in magnetic field

Abstract Magnetic field forming is a promising method to produce high quality ferromagnetic materials. In this process, magnetic powder is formed in the high magnetic flux by the metal injection molding process. However the parameter of this process is very complicated and it is still difficult to obtain the optimum forming conditions. The analytical method is very effective tool to make such optimum forming design and to investigate the mechanism of the magnetic powder flow under applied magnetic field and pressing. We developed the coupling method of pressing load with magnetic field to simulate the magnetic field forming. In this method, granular modeling is utilized to simulate the mechanical behavior of the powder particles and the magnetic field is considered as a body force. In the numerical example, we analyzed the difference of the magnetic powder flow for pressing schedule and the preferred orientation of magnetizing of the magnetic powder is taken into account in the particle modeling.

Thermal and mechanical coupling in granular modeling for metal injection molding

Abstract Metal injection molding (MIM) employs viscous thermoplastic polymer materials (binders)_ with metallic powders to improve flowability and formability. It is essential to be able to describe the behavior of such mixed materials, for this purpose a new granular model being proposed to deal with the powder characteristics and mechanics. The composite element is designed to consider both elasticity and viscosity for powder particles and binders. A thermal and mechanical coupling effect is introduced directly to describe the cooling process. Numerical results demonstrate the effectiveness and validity of the presently-developed granular modeling in dealing with the various phenomena appearing in the MIM process.

Three-dimensional granular modeling for metallic powder compaction and flow analysis

Abstract Powder is a popular state of material for many industries. In powder metallurgy, it is important to know the behavior of the powder under applied stress to ensure accurate design and good quality. However, the mechanical behaviors of powder is not well understood. The authors consider that this is due in part to the difficulty in handling powder numerically. To investigate the fundamental mechanism of powder behavior, numerical simulation of the behavior of powder under mechanical compression and under applied vibration has been performed. To describe the mechanical behavior of powder in practical forming, granular modeling is a powerful tool. Allowing for the effect of three-dimensionality in the compaction and flowability is essential for precise description of powder behavior. In this paper, three-dimensional granular modeling is proposed and developed for metallic powder compaction and flow analysis. The validity of the method is demonstrated. Formulations based on the three-dimensional direct ball-element method (DBEM-3D) are presented and discussed briefly. In the numerical simulation, static powder compaction and vibration-induced powder behavior considered. The differences between two- and three-dimensional calculations are discussed.

Materials evaluation of pvd/cvd coated wc/co superhard alloys by the ultrasonic microscopy

Abstract CVD/PVD coating or ion-injection processes have become one of the most important and significant key-technologies to protect surface of mechanical or electric parts or tools against various wear mechanisms and to prolong the life-time of actively working materials; TiN or other ceramic coated WC/Co is the typical tool materials to be used as the chip or die materials in the metal forming. For the optimum design of these materials and the related materials processes, new quantitative evaluation methodology is indispensable; in the present paper, the first introduction of ultrasonic microscopy oriented materials evaluation will be stated with comments on the determination of both elastic and elasto-plastic properties of TiN/TiC/Ti(CN) coated WC/Co cermets. Through discussions over the measured and evaluated elastic or elasto-plastic responses of coated cermets, the reliability of the present materials evaluation methods will be considered.

Roll pass evaluation for hot shape rolling processes

Abstract Since the complex shaped caliber rolling usually takes place in hot operation, three dimensional mechanical behavior coupled with the heat transfer in and around the billet must be taken into account for accurate evaluation of the roll pass system. In the present study, the authors propose a new simulation approach to deal with the above coupling problem: the deformation mode method for the three dimenional deformation in the steady-state rolling process, and the two dimensional boundary element method for radiation and convection heat transfer between mill stands. Furthermore, to deal with temperature history in plastic working, heat generation by plastic deformation and friction work and heat transfer between rolls and billet are both taken into account in every incremental reduction. As an example, the butterfly roll pass system is taken in the actual angle steel rolling. It is found that (1) the mechanical behavior and characteristics can be discussed by the calculated metal flow, strain and temperature distributions in the whole roll pass system, and (2) the numerically estimated cross-sectional shapes after rolling are in fairly good agreement with the experimental measurements in the actual processing. The above example demonstrates the validity and effectiveness of the present modelling even for the industrial shape rolling process.

MECHANICAL BEHAVIOR OF POWDER PARTICLE ON THE APPLIED VIBRATION

Powder is the popular state of material for the many parts of industries. In the powder metallurgy, it is important to know the powder behavior under applied stress for the accurate design and good quality assurance. But the mechanical behaviors of it has not been well known. We consider this is from the difficulty of handling powder numerically. To investigate the fundamental mechanism of powder behaviors, we performed experiment and numerical analysis for the powders on the applied vibration. In this experiment specimens of powder are on the vertical vibrator. And the dynamic location of powder particle are observed by a laser-displacement meter, at the same time dynamic flow of powder are observed by a high-speed video camera. From this experiment we found that the powder flow can be classified to several patterns and those patterns are strongly depending on the frequency and amplitude of applied vibration, particle size, and grain size distribution of the powder. In the numerical analysis we used the particle model. This calculation model refer to Cundall’s Distinct Element Method. We performed several numerical analysis on various conditions. From the result we considered the major parameter which determine the flowing pattern is the frictional conditions.

Composite finite elements for rigid-plastic analysis

Abstract In the conventional rigid-plastic finite element analysis, quadrilateral elements or brick-type elements are widely used for two- or three-dimensional simulations in rolling or forging. Through some mathematical studies and numerical tests of errors, the quadrilateral element family, especially the 4-node element with bilinear interpolation for incremental displacement or velocity and constant for pressure, is found to be unsuitable for elasto-plastic or rigid-plastic analyses with large deformations; this type of element often causes large local errors for shear components of strains and stresses, especially in stress concentration problems or in plastic forming problems with local distortion of elements. An alternative family of elements will be proposed and discussed for two- and three-dimensional rigid-plastic simulation in rolling or forging. Since the LBB condition for incompressibility is imposed on the employed velocity interpolations in construction of the adequate finite elements models, the use of conventional triangular elements is prohibited in the rigid-plastic plane strain, axisymmetric or three-dimensional analyses, where the incompressibility condition of plastic strain or strain rate or the volume constancy should be explicitly evaluated by the variational equation or the weak form. Our approach is based on the mixed finite element method where both velocity and pressure are interpolated to satisfy the LBB condition and to become robust for local element distortion. In the present paper, a list of candidate mixed type finite element pairs other than the four-node element will be shown with some comments on their characteristics and features. Special attention will be paid to the composite-type finite element schemes for two- and three-dimensional problems; in particular, the inner-mode composite element family is described with respect to their fundamental behavior in rigid-plasticity. In principle, our developing elements are free from shear/membrane locking and from contamination by zero-energy modes, and stable and robust against the folding behavior of the corner points. Furthermore, the introduced pressure can be excluded from the final element equations by the static condensation or the penalty function method. Through the basic numerical tests for upsetting problems, accuracy and convergency will be evaluated for these elements. Finally, some further examples on the complete automatic mesh control will be employed to show the potential of these elements for adaptive mesh control.

Shock reactive synthesis of TiAl

Abstract The shock reactive synthesis (SRS) processing was developed to yield bulk solid titanium aluminides in a non-equilibrium phase structure. From blended element powder compacts with a composition of Ti50A150, TiAl is directly synthesized without porosities. The shock-induced reactions can be macroscopically described by SRS-diagram, and the effect of the detonation condition and the green compact porosity on the constituent phases and microstructure of synthesized materials are also discussed on this diagram. In the reactive zone of this diagram, the abundance ratio of α 2 to γ in the α 2 γ two-phase synthesized materials can be controlled from the equilibrium ratio to the α 2 single phase by increasing the detonation velocity and/or the porosity of compact. By using multi-layered samples with a sandwich structure of Ti and Al porous discs, the fundamental mechanism of shock-induced reactions can be investigated to clarify the role of high speed mixing and homogenization of titanium and aluminum in the reaction process at the passage of shock wave.

Shock induced reactions of titanium aluminides from mechanically alloyed precursor.

In the planar shock reactive synthesis from element powder mixture with 1Ti+1Al by one-stage gun, only TiAl3 is synthesized with large amount of residual Ti and Al. The pretreated powders by our developed mechanical alloying system or the MA-precursors are fully reacted into two phase binary system (TiAl+Ti3Al) with little amount of residual titanium and without TiAl3 and residual aluminum. For varying the pretreated state, a role of this pretreatment by mechanical alloying on shock induced reaction is discussed with precise microstructural observation of synthesized materials.