Mechanical alloying and consolidation of copper-iron-silicon carbide nanocomposites

Mechanical alloying, cold pressing, and sintering were used for synthesizing bulk copper, copper-iron, and copper-iron-silicon carbide nanomaterials. The precipitation of iron during sintering of the supersaturated mechanically alloyed powder significantly enhanced the thermal stability of the nanocomposite against grain growth. Moreover, the hardness of sintered composites was found to increase with increasing milling time, which was attributed to the work-hardening, crystallite refinement, and increasing the relative density (decrease in porosity). Although the addition of silicon carbide did not affect the mean crystallite size of the bulk samples, it effectively increased the hardness of the nanocomposite based on its composite strengthening effect.     

Microstructure and mechanical properties of spark plasma sintered titanium‐added copper/reduced graphene oxide composites

Copper matrix composites were fabricated through mixing fixed amount of reduced graphene oxide and the different amounts of titanium. The dried copper/titanium/reduced graphene oxide mixture powders were firstly obtained by the wet‐mixing process, and then the spark plasma sintering process realized their faster densification. In the as‐sintered bulk composites, the layered reduced graphene oxide network, uniform titanium particles and copper‐titanium solid solution are observed in copper matrix. Investigations on mechanical properties show that the as‐prepared bulk composites exhibit the hardness and compressive yield strength compared with single reduced graphene oxide added composites. Increased titanium addition resulted into higher hardness and strength. The relevant formation and failure mechanisms of the composites and their influence on mechanical properties were discussed.     

Evaluation of mixed oxide formation and sintering behavior in thermal barrier coatings on nickel‐based superalloy

Thermal barrier coatings are widely used in aircraft turbines to protect nickel‐based superalloys from the effect of high temperature oxidation and hot corrosion. In this study, both NiCrAlY bond coat and yttria‐stabilized zirconia top coat were deposited using atmospheric plasma spray technique. After coating production, specimens were exposed to oxidation in air atmosphere at 900 °C, 1000 °C and 1100 °C for different periods of time up to 50 h. Microstructural transformations in the ceramic top coat and growth behavior of the thermally grown oxide layer were examined using scanning electron microscopy, porosity calculation, elemental mapping and hardness measurement. Formation of different types of oxides in the thermally grown oxide layer shows that this process strongly depends on deposition technique as well as on oxidation time and temperature. Hardness values of the top coat increased with a decrease in the porosity of the top coat. Uniformity and homogeneity of the thermally grown oxide layer and densification of the top coat were evaluated in terms of the structural durability of thermal barrier coating systems.     

Use of Ti in hard metal alloys – Part II: mechanical properties

WC‐Co hard metal is a material of high hardness, high compressive strength and wear resistance while maintaining good toughness and thermal stability. Samples of nanosized WC powders with 10 wt% Co, WC‐10 wt% Ti, WC‐9 wt% Ti‐1 wt% Co were cold pressed at 200 MPa and sintered at 1500°C during 1 hour under vacuum of 10^–2 mbar. The characterization of the sintered materials was performed by the measurements of densification, HV30 hardness, fracture toughness and compression strength. The results showed that it is possible to process a hard metal through a Powder Metallurgical conventional route from nanoscaled WC grains, using Ti (or a Ti‐Co mixture) as a binder phase, with good mechanical properties.     

Das Sintern in der Prozesskette des Pulverspritzgießens

This contribution relates shrinkage of porous bodies while sintering directly to diminution of internal surface. Based on dilatometric measurements, the kinetic model presented predicts shrinkage for any given temperature‐time history. In addition to the known concept of the master sintering curve (MSC), different powder size distributions, different initial densities and an activation energy varying during the course of sintering can be taken into account. In the early stage of sintering, measured shrinkage differs from values obtained by regression according to the models presented in a systematic manner. The differences are ascribed to transformations occurring before and in the course of sintering. In this case we propose amending of sintering models by incorporating transformations influencing the rate of sintering.     

The effect of yttrium oxide in hydroxyapatite/aluminum oxide hybrid biocomposite materials: Phase,mechanical and morphological evaluation

This study presents the fabrication and characterization of composite materials of hydroxyapatite and aluminum oxide. Hydroxyapatite powder was obtained from bovine bones via conventional calcination routine. Although hydroxyapatite shows great biocompatibility with the human body, its applications are limited to non‐load bearing areas. For this purpose, fine powders of hydroxyapatite/alumina were admixed with 1 and 5 wt.% yittria. Powder‐compacts were sintered by two‐step sintering route by increasing temperature to 1550 °C for 2 h and then sintering at 1450 °C for 4 h. The effect of increasing yittria content on sintering behavior and mechanical properties was investigated in biocomposite hybrid materials.     

Experimentelle und numerische Untersuchungen zur Kennzeichnung von Sinterteilen mittels gezielt eingebrachter Fremdpartikel

Experimental und numerical investigation on the marking of sintered parts by the targeted application of particles Sintered parts from steel as well as light metal alloys are becoming popular in many industrial sectors due to their advantageous product properties. Beside the good utilization of raw material and the variability in alloying the sinter technology offers the opportunity to mark parts in a unique and invisible manner. Spheric particles are used as information carrier. A quadratic 4x4 matrix with a maximum of 16 particles is placed inside a sinter part for first experiments. The defined places and number of particles result in an identification number. After sintering process the two materials are inseparably connected. The readout of the data is realized with x‐ray or computer tomography due to different physical properties of the particles and the powder material.     

Mikrowellenangepasstes Sintern von Ferriten

Microwave‐aligned sintering of ferrites Sintering of ceramics using microwaves can lead to improved material quality and productivity. The technical implementation of the microwave technology is still lacking because of different temperature distribution inside the specimen due to volumetric heating compared to conventional sintering. The development of microwave‐aligned processes require the determination of the inside temperature distribution by means of mathematic concepts. Therefore a simplified model was set up which consists of a thermodynamic and a heat source model. Heat transfer within the specimen and the periphery will be included. To govern the heat process this model was integrated into a control algorithm. The control concept was proven by experiments using nickel‐zinc‐ferrite. The system provides effective protection against thermal‐runway and incorrect temperature differences in the specimen. Simultaneously changes of temperature depending electromagnetic and thermodynamic material properties can be counter steered.