摘要:

Martensitic Cr-alloyed high-temperature materials offer interesting opportunities for design and construction of advanced power plants. An extensive research programme has been carried out at the Research Centre of the Belgian Welding Institute and Laborelec on martensitic 12% Cr steel for gaining a better understanding of the failure mode and the deformation mechanism of welded joints under uniaxial and multiaxial loads. A large number of pipe girth welds were realized by three Belgian manufacturers (Cockerill Mechanical Industries, Fabricom and Mannesmann-Carnoy). Different filler metals were used and the influence of the welding regime (austenitic and martensitic), the post-weld heat treatment (PWHT) (single or double) and the base metal wall thickness on the high-temperature properties of the different weldments was evaluated. It was found that the creep properties of a 12% Cr weldment are not influenced by the welding regime and the base metal wall thickness. As would be expected, the creep strengths of the original 12% Cr base metal as well as the temperature of the PWHT have some effect. The existence of a typical failure in the intercritical zone (type IV region) is demonstrated and explained. The consequences for the design of welded 12% Cr components are indicated. More recently the research was extended towards improved 9% Cr steel (T91). A rather small preliminary programme for the orientation of further research showed a similar failure location as for 12% Cr steel, although the observed loss in strength of the weldment compared to the base metal tended to be considerably lower. The so-called‘half-tempering’treatment was tried out and the effect on the creep strength of the weldment is shown. A more fundamental national research programme on P91 steel has been established and is actually running.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689658

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

An investigation has been made into the friction and wear of titanium-nitride-coated 321 stainless steel during like-on-like sliding contact in carbon dioxide environments at temperatures to 500°C, with emphasis on the synergistic interactions between oxidation and mechanical wear. Tests have been made on both as-received surfaces and those present after long-term oxidation in CO2/1%CO at 450–700°C. During sliding at 20–300°C, the presence of a thin (2-3μm) titanium nitride coating on the stainless steel surfaces resulted in much lower coefficients of friction and wear rates than were recorded for similar uncoated specimens. In the latter case, metal-metal contact led to extensive deformation and ploughing of the surfaces and a high wear rate, while the presence of the coating eliminated such contact, at least in the early stages. However, the extent of wear was sufficient to cause thinning of the coating until, eventually, it was penetrated and the coefficient of friction and wear rate increased considerably. At 500°C, oxidation of the stainless steel surfaces resulted in the development of oxide‘glaze’on the uncoated specimens and much reduced friction and wear rates. Similarly, for the coated specimens, oxidation of both the titanium nitride coating and any exposed steel substrate ensured that low friction and wear were maintained for extended periods. Long-term oxidation of both coated and uncoated specimens at 550 and 700°C enabled a wear-protective oxide to develop rapidly on subsequent sliding at 300°C, giving reduced friction and wear. This is accounted for in terms of the beneficial effects of oxides in protecting surfaces under sliding wear conditions.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689659

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The corrosion behaviour of several alloys and of various protective coatings on 15Mo3 has been tested under conditions found in coal gasification processes. The experiments showed that of all the uncoated samples tested, only AISI 310 has a promising resistance to these corrosive atmospheres. On most of the other materials spalling of the corrosion products was observed. The main corrosion products were iron, chromium and nickel sulphides, chromium oxide and chromium carbide. Materials protected by different coatings showed very good corrosion resistance when coated by plasma spraying with FeCrAl, containing small amounts of yttrium. Good resistance by coating against the corrosion was also observed for alloys chromized by pack cementation. A small amount of vanadium added to the pack improved the quality of the diffusion coating considerably.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689660

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The viability of advanced viscoplastic models for nonlinear finite element analyses of structural components is investigated. Several uniaxial and a multiaxial problem are analysed by using the finite element implementation of Freed's viscoplastic model. Good agreement between the experimental and calculated uniaxial results validates the finite element implementation and gives confidence to apply it to more complex multiaxial problems. A comparison of results for a sample structural component (the cowl lip of a hypersonic engine inlet) with the earlier elastic, elastic-plastic, and elastic-plastic-creep analyses available in the literature shows that the elastic-viscoplastic analyses yield more reasonable stress and strain distributions. Finally, the versatility of the finite-element-based solution technology presented here is demonstrated by applying it to another viscoplastic model.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689661

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The effects of oxidation and hot corrosion on the high-temperature strength of reaction-sintered and hot-pressed silicon-nitride-based ceramics have been investigated. A strength reduction and static- fatigue sensitivity in the temperature range 700–900°C were observed in the tests in air and in the presence of salts. Silicon-nitride-based ceramics were found to be stress-corrosion sensitive over a specified temperature interval. Sample failure at lower loads was shown to result from both corrosion-induced flaws in the ceramic's surface layer and stress-corrosion cracking. Some methods for ceramic protection against stress corrosion are proposed.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689662

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The mechanical processes involved in thermal fatigue degradation of a cast-turbine-blade material have been studied by an induction heating procedure coupled with an advanced AC potential drop system (ACPD). In particular, three temperature histories (cycle type) were investigated using double-edge wedge specimens of cast IN-100 nickel base alloy. The respective stress-strain histories, as determined from thermo-elasto-plastic finite element analyses, are presented. Depending upon strain history, two modes of surface degradation were observed: scalloping and through-thickness cracking of a uniform oxide layer. The degree of scalloping was shown to depend on the magnitude of compressive strain at the surface. Severe scalloping was observed after 3000 thermal cycles between peak strains of -0.48% at 1050°C and +0.08% at 400°C. More than 3000 cycles between peak strains of -0.24% at 1050 deg;C and 0.23% at 400°C did not produce scalloping. The number of cycles to crack initiation was found to correlate with peak compressive strain. The findings were shown to be consistent with a mechanism for scallop initiation and growth involving cyclic oxide cracking and cyclic ratchetting. Mathematical formulations to model the observed damage mechanisms are proposed. The implementation of these damage evolutive laws into design and lifing procedures is discussed.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689663

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Zirconia thermal barrier coatings are now essentially limited to‘clean fuel’engines because the commonly used stabilizers for zirconia (CaO, MgO, Y2O3) react with the sulphur and vanadium contaminants contained in low quality fuel. Corrosion-resistant stabilizers for zirconia have been sought as a response to this problem, with ceria (CeO2) and, more recently, scandia (SC2O3) and india (ln2O3) being identified. This paper outlines some of the concepts, chemical reactions and thermodynamics that are involved in the development of hot-corrosion-resistant zirconia ceramics.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689664

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689665

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689666

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor