Thermal Resistance Of Material Research Articles

Fabrication and Properties of Functionally Gradient Materials

Functionally Gradient Materials (FGMs) characterized by the material having continuously varying material property from one surface to the other, have been prepared using gas, liquid or solid as starting material via several methods such as CVD, PVD, ion plating, plasma spraying, sintering or self-propagating high temperature synthesis. The initial research in the development of the Functionally Gradient Materials was to obtain a superior thermal resistant composite material having excellent thermal barrier characteristics, thermal resistance and thermal stress relaxation, however, the recent trend in the development study is to consider FGM as a possible material superior in not only thermal characteristics but also in electrical, optical and chemical functions. In the application of Functionally Gradient Materials for the thermal barrier material the concentration of the dispersion phase is gradually varied in the material to obtain the required thermal stress relaxation.

High heat flux test by high current and low energy electron beam

High thermal shock resistance is required for plasma facing materials in nuclear fusion devices. Graphite and carbon based composites are the primary candidates for high heat flux materials to be used for limiter or armor plates at present. In this study, thermal shock tests of commercially available isotropic graphite were conducted using a hot hollow cathode type electron gun with a high current (200 A) and low voltage (50 V). Heat flux was 1–2 kW/cm 2 , flux diameter was 18 mm, and specimen size was 25 mm×25 mm×1 mm. Specimens fractured into 2 or 3 pieces within l s of heat load duration. A magnitude of flux when a specimen fractured for l s of heat load duration was used as a measure of thermal shock resistance. The thermal shock resistance of the most anisotropic sample was the highest in this experiment. Correlations between thermal shock resistance and various material properties were examined among samples, except the anisotropic samples. The thermal shock resistance was higher for samples with lower fracture strength and lower apparent density and larger pore size. This result is not in accordance with a simple model based on thermo-elastic theory. It may suggest that thermal shock resistance is controlled by a crack propagation process rather than a crack initiation process.

Frictional thermal resistance of materials produced by metal powder rolling

The operating characteristics of frictional materials produced by powder rolling with subsequent sintering in the “free” state are comparable with those of materials produced by pressing with subsequent sintering under pressure. There are no qualitative differences in the mechanisms of friction and wear of these materials. Quantitatively, results are influenced by the porosity of materials and sintering conditions chosen.

The Vickers Indentation Technique Applied ToThe Evaluation Of Thermal Transient Stresses DueTo Quenching Of Brittle Materials

Use is made of the domain of stable extension of the Vickers indentation crack system in order to investigate both the thermal shock resistance materials and the thermal transient stresses which appear during quenching of brittle materials. The equivalency of thermally and mechanically induced stresses is assumed such as to describe the relative increase in length of the radial crack during quenching. This approach is checked in using two different glass ceramics, various quenching conditions and sample sizes. Finally is the increase in length of Vickers indentation cracks measured or samples loaded in bending and a maximum of the thermal transient stress evaluated. This offers the mean to approach an effective heat transfer coefficient.

RESEARCH IN MACHINING HIGH STRENGTH MATERIALS AT ELEVATED TEMPERATURES

SUMMARY Tests were run with high strength thermal-resistant work materials selected by surveying U.S. aircraft engineering companies to find representative types of materials presenting problems in convential machining. Each material tested had two different heat treatment procedures. Tests were conducted in orthogonal and conventional turning, in milling and in drilling operations using different methods of workpiece heating. Information was obtained on tool life—cutting speed relationships, tool temperatures and forces, chip formation and related quantites for a range of work temperatures. Metallographic studies of hot-machined parts were carried out and the effects of the process on workpiece geometry are discussed. Assessment of workpiece heating methods will be the subject of a further paper.