Radu L. Orban

Experimental Study and Neural Network Modeling of the Stability of Powder Injection Molding Feedstocks

Abstract Due to their complex rheological behavior, feedstocks for powder injection molding (PIM) may exhibit non-homogeneous flow and separation. This can produce defects of green parts during mold filling, resulting in their cracking and warpage during debinding and sintering, and ultimately in poor physical and mechanical properties of the final part. An experimental rheological study has been performed to evaluate the influence of solids loading, shear rate, and powder particle size on feedstock stability. A micro-rheological explanation is given for the macroscopic effect of separation, and an instability index has been defined to describe quantitatively the threshold beyond which the variation of viscosity becomes unacceptable for PIM purposes. A neural network model has been developed for predicting the viscosity of feedstocks made from binary blends, when the powder characteristics, blend composition, and shear rate are known. The system enables determination of the process parameters for which powder-binder separation occurs in a given feedstock.

Thermal, Mechanical and Electrical Properties of High Density Polyethylene Composites Reinforced with Copper Powder

The thermal conductivity, electrical conductivity and mechanical properties such as tensile strength, elongation, modulus of elasticity, were experimentally investigated. Thermal and electrical conductivity measurements were performed up to filler concentration of 30 vol.%. The mechanical properties of high density polyethylene filled with up to 30 vol.% Cu particles were investigated. The tensile strength, elongation and toughness decreased with increasing Cu powder content. This was attributed to the introduction of discontinuities in the polymer structure in which modulus of elasticity increased with increasing the copper content.

Shape memory alloys for MEMS components made by powder metallurgy processes

The paper presents some research results in the field of NiTi shape memory alloys made through powder metallurgy techniques. These techniques allow the obtaining of materials with savings of energy and time due to use of NiTi heat formation for the material synthesis. Ni-Ti, Ni-Ti-Fe and Ni-Ti-Cu alloys were performed by self propagation high temperature synthesis, starting from elemental powders. From the mixtures of powders with corresponding chemical compositions were made green compacts by cold pressing with 400, 500 and 600 MPa which were then synthetized at 950, 1000 and 1050degC for 1 hour, in argon atmosphere. The obtained materials were investigated in order to detect the phase formation and to evidence the microstructural aspects. The martensitic transformation was evidenced by differential scanning calorimetry. As synthetised materials it were shown that only the Ni-Ti-Cu materials exhibits shape memory effects.

Metallic Porous Parts for Electronics Devices Cooling

The paper presents some results regarding the obtaining of some copper heat pipes with a porous copper internal layer for electronic components cooling. The heat pipes were realized by sintering of spherical copper powders of 90-125 mum size directly on the internal side of a copper pipe of 18 mm in diameter. The obtained pipes were then brazed in order to obtain a heat pipe of 0.5 m in length. After that, the heat pipe was sealed and filled with a small quantity of distilled water as working fluid. To establish the total heat transport coefficient and the thermal flow transferred at the evaporator, some external devices were realized to allow the heating of the evaporator and the cooling of the condenser. Water heat pipes are explored in the intermediate temperature range of 303 up to 500 K. Test data are reported for copper water heat pipe, which was tested under different orientations. The obtained results show that the water heat pipe has a good thermal transfer performance in the temperatures range between 345 and 463 K

Shape Memory NiTi Alloys Obtained by Powder Metallurgy Route

The effect of Fe, respective Cu, additions as substitute for Ni in NiTi shape memory alloys (SMAs) on the delaying of its phase transition and narrowing hysteresis are well known, NiTi-Fe and NiTi-Cu SMAs having applications especially to the actuators that require such properties. These SMAs are currently produced by conventional melting methods, which are energo-intensive and impose very severe processing conditions to avoid contamination. The results of researches presented in this paper prove the possibility of these SMAs obtaining by powder metallurgy via reactive sintering – more advantageous from both technical and economic point of view. A beneficial effect on both sintering and homogeneity of the obtained SMAs proved to have a controlled mechanical alloying applied to powder mixture before compacting and sintering.

NiAl Behavior at Plasma Spray Deposition

The behavior of stoichiometric and near-stoichiometric NiAl at plasma spray deposition, without and with a bond coat, for coating layers realization on a low alloyed steel substrate has been investigated and is presented. In all variants, NiAl particle melting and their welding at the impact with substrate were observed. Furthermore, a relatively compact and adherent coating layer was formed and the NiAl was found to maintain its stability. These are all important factors for assuring the coating layer oxidation and corrosion resistance. Good results from the coating structure and adherence to the substrate points of view were obtained for the 45:55 Ni:Al composition, without a bond coat but adopting an Ar protective surrounding of plasma jet. The high resistance to corrosion of 45:55 NiAl composition was further validated through corrosion tests.

NiAl Oxidation and Corrosion Resistant Coatings Obtained by Thermal Spraying

There are investigated the possibilities to avoid or at least to reduce the Al2O3 scales formation on NiAl powder particles at its plasma spray deposition on steel substrates. The optimum processing parameters and the necessity to surround the plasma jet by an inert gas have been established. In appropriate processing conditions, the obtained coating layer is formed by flattened particles, welded together and to the substrate, proving their melting during spraying. It is dense and adherent, consisting of NiAl with only small Al2O3 inclusions, proving the NiAl stability preserving without decomposition or a notable oxidation, as premises of its desired functionality achievement.

Mechanical, Thermal and Electrical Properties of Acrilonitril Butadiene Styrene (ABS) Composites Filled with Bronze Powder

This article reports on an experimental study of the mechanical, thermal and electrical properties of bronze-ABS composites containing 5, 10, 20, 30 vol.% of bronze powder. The mechanical properties such as ultimate tensile strength, elongation at fracture, modulus of elasticity, melt flow rate (MFR), hardness, thermal conductivity, electrical conductivity of bronze powder filler embedded in a ABS matrix were experimentally investigated. Thermal and electrical conductivity measurements were performed up to a filler concentration of 30 vol.%. The tensile strength, elongation, MFR values continuously decreased with increasing the bronze powder content. However, modulus of elasticity and hardness increased with increasing the bronze content. Thermal and electrical conductivity of the composites was found to be higher for ABS-20 vol.% bronze composites than that of the other composites.

Analysis of Functional Properties of Cu-Al2O3 Particulate Reinforced Composites. A First Assessment: Elaboration

The possibilities of Cu-Al2O3 particulate reinforced composites, of competitive functional properties, processing by the classical powder metallurgy route have been investigated taking into consideration its known technical and economical advantages in respect to the known worldwide investigated technological routes of their processing. The adopted compositions, of (5.0÷20.0) [vol.%] Al2O3, were selected in agreement with published data for a large range of applications. Pharmaceutical homogenization method applied for powder mixtures preparation proved to assure a high homogeneity, evidenced by SEM and EDS analyses. Their determined compressibility has shown that, for all compositions, the obtainable compactness is very close to that of pure Cu (even over 94 %). Cold uniaxial compaction at 500 and 700 MPa, and subsequent sintering in argon of high purity at 800 °C for 45 and 60 min have been adopted for composites realization. The performed analysis of the compacting pressure and sintering time influence on the composite compactness proved that, beside the above specified values obtaining for 700 MPa and 60 minute processing parameters, high enough values, acceptable for numerous applications, can be also obtained at 500 MPa and 60 or even 45 minutes. Finally, microstructural analysis highlighted that, by the adopted processing conditions, a high uniformity of Al2O3 particles distribution in the Cu matrix can been assured, both creating premises for obtaining good functional properties of Cu-Al2O3 composites, proving the competitiveness of the investigated PM route for their elaboration.

SHS Processing of NiTi-Nb Smart Alloys

Nb additions to NiTi smart alloys are known to lead to the PTT-hysteresis broadening and transformation temperatures raising – required in numerous applications. As Nb has a high affinity for oxygen, NiTi-Nb alloys processing by powder metallurgy, via SHS, from elemental Ni-Ti-Nb powder mixtures, seems to be more advantageous and cost-effective than by classical one. However, its application encounters difficulties determined by the NiTi higher Gibbs Free Energy of Formation than of Ni3Ti and NiTi2, possible Ni-Nb compounds formation, Nb acting as diluent in SHS. This research proved the possibility to overcome these difficulties and of NiTi-Nb alloys obtaining by SHS using energetically activated powder mixture by controlled Mechanical Alloying. Also, it was proved the possibility to reduce Nb content from the common one of 9 at.% to 5 at.% without a significant effect of transformation temperatures and hysteresis decreasing.