ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.177

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.179

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.182

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.210

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.212

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractOptimisation of thermal spraying, as for generic polymers, produces thermosets in the uncured condition with unsatisfactory engineering properties. The present paper develops a theoretical process modelfor thermoset reactive deposition, based on heat transfer mechanisms, which enables temperature profiles to be generated as a function of process variables. The model predicts that crosslinking can not take place in in flight precursor particles, isolated splats, or deposits without substrate preheating. It shows that the difficulty in achieving satisfactory properties is a result of the rapid heat flow to the substrate, which suppresses the crosslinking reaction. The model is applied to identify methods of enhancing the engineering properties of thermosets and indicates that substrate preheating, ceramic undercoats, and rapid curing agents can promote the curing reaction during thermal spraying. An experimental technique to evaluate the degree of crosslinking in the deposits from enthalpy determinations is developed. The experimental work, which consisted of differential scanning calorimetry and tribological measurements, is in agreement with the theoretical model and the predicted process route was successful in producing thermosets that were 85% cured in situ by reactive deposition.

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.215

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractA series of experiments has been carried out to investigate the fibre optic Nd–YAG laser cladding of C–Mn steel with preplaced Hastelloy C powder. The beam from a pulsed Nd–YAG laser, operating at an average output power of 300 Jt: was transmitted to the workpiece via a step index glass fibre of length 5 m and core diameter 600μm. A range of laser pulse energies, durations, and repetition rates was investigated forseveral focal length positions to determine their effect on clad layer formation and integrity. It was found that, for a limited range of process parameters, metallurgically sound clad layers up to 500μm thick could be formed with less than 10% dilution by the substrate.

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.223

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractPlasma sprayed yttria stabilised zirconia (YSZ) coatings were investigated to assess the factors influencing their durability during thermal cycling. For any given powder, the best performance was found to be achieved at an optimum plasma arc current, all other spray parameters being held constant. The YSZ overlayer thickness was found to be an important lifetime determining factor. Use of a NiCoCrAlY bond coat instead of Ni–Cr led to a substantial improvement in coating lifetime, with the enhancement provided by NiCoCr AlY becoming more pronounced with increasing porosity level of the ceramic overlayer. A post-coating heat treatment was also found to be beneficial to coating longevity. The relative ranking of magnesium zirconate and YSZ coatings was found to depend upon the thermal cycle adopted during testing, which has important implications in designing accelerated tests to evaluate coating performance.

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.233

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractThe nitriding rate of a high chromium, high manganese austenitic steel has been found to exhibit abnormalbehaviour similar to that of austenitic stainless steels, i.e. a sudden decrease of the rate at about 870 K; marked acceleration between 670 and 870 K; a discontinuity at about 670 K; and formation of a nitrogen supersaturated nitrided layer below 670 K. These results require a new explanation, since previous theories address the abnormalities in austenitic stainless steels only. Accelerated nitriding is discussed with reference to the free energy of formation of chromium nitrides (Cr2N and CrN) on a T–∆G°diagram. The sudden decrease of the rate is attributed to the termination of accelerated nitriding.

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.240

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractCoating thickness distribution, surface appearance, and grain size are known to be important factors in determining the effectiveness of coatings used in the production of printed circuit boards. Square wave unipolar pulse and bipolar pulse reverse current electroplating of copper using an acid copper electrolyte has been reported to provide a coating superior to that produced by dc under certain pulsing conditions. The present paper describes a systematic assessment of the properties of electrodeposited coatings produced under unipolar pulse and bipolar pulse reverse current plating conditions. Results show that the overall coating uniformity under pulsing conditions is better than that obtained using dc plating. The surface texture of the coatings is shown to be strongly dependent on the pulsing conditions and is especially affected by bipolar pulse reverse conditions.

ISSN:0267-0844    

DOI:10.1179/sur.1995.11.3.246

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor