摘要:

AbstractIt is relatively recently that thermotropic liquid crystal polymers for load bearing applications have become commercially available. These materials possess good mechanical properties and excellent processability and are intended for use at elevated temperatures in harsh chemical environments. In this paper, the phenomenon of liquid crystallinity is described and the way in which it improves the mechanical properties and processability of polymers is explained. The synthetic strategies involved in obtaining nematic mesophases in polyesters are discussed fully, particularly those involved in the synthesis of commercially available materials. The future of these new types of engineering thermoplastic will depend on cost and on the appropriate application of the unique properties they offer.MST/875

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.309

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractAn electron metallographic examination has been performed on samples of a 1Cr–1Mo–0·75V (Ti,B) bolting steel (Durehete 1055) as part of a long term creep programme. The apparently anomalous carbide composition results have been rationalised by the use of pseudoternary phase diagrams. This novel method of presenting the alloy carbide composition data enables the changes accompanying service exposure to be described. It is obvious that the conventional thermodynamic order of stabilities does not obtain over the entire range of temperatures experienced by this alloy.MST/914

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.323

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractPrecipitation in a high nitrogen austenitic stainless steel of the Nitronic series has been studied. Above a critical nitrogen concentration, cellular precipitation is observed together with formation of Cr2N as a general precipitate and intragranular precipitation of Z phase (Cr2Nb2N2). The nature of cellular precipitation has been studied using constant activity aging in nitrogen and the characteristics of the process have been examined using X-ray diffraction and electron microscopy. The cellular precipitation process is shown to be consistent with a model based on long range diffusion of nitrogen and equilibrium between the gas phase and steel matrix. The solubility of nitrogen in austenite in equilibrium with the gas phase or with Cr2N precipitates is consistent with published data.MST/917

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.328

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe effects of solution treatment temperature and cooling rate, carbon content, and aging at 600°C on the precipitation and grain boundary composition of AISI type 316 stainless steel were investigated. No matrix precipitation was observed even in a high carbon cast aged for 1000 h. Carbides of M23C6type were the only precipitates observed and these formed on grain boundaries. Nucleation of a second phase in these solution treated specimens was difficult, despite the carbon supersaturation. The grain boundary regions were investigated using high spatial resolution X-ray analysis to show that chromium depleted and nickel enriched zones formed when grain boundary carbides occurred. The behaviour of molybdenum was more complex; it segregated strongly to grain boundaries either during a slow cool from the solution treatment temperature or during aging, but was also incorporated into any carbides that formed.MST/890

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.333

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe sequence of precipitation and its kinetics in 17–4 PH (precipitation hardening) stainless steel were studied by observing the electrical resistivity and microstructure of the alloy during isothermal aging at various temperatures in the range 320–600°C. By the absence of an incubation period for the onset of precipitation it is shown that there is no free energy barrier to nucleation. The electrical resistivity of the specimen decreased on prolonged aging approaching a steady value asymptotically with time. The alloys aged above 550°C were found to have higher final resistivity values than those aged at lower temperatures. By transmission electron microscopy, local reversion of the martensite to austenite, attributed to enhanced diffusion and concentration of copper atoms at the lath boundaries, was revealed in the specimens aged at temperatures above 550°C. The kinetics of precipitation in the system obeyed the Johnson–Mehl equation. The activation energy Q of the precipitation process was estimated to be 112·2±3·6 kJ mol−lfrom the resistivity measurements. This may be understood in terms of an enhanced diffusion of copper atoms in the supersaturated matrix caused by a higher dislocation density and a higher concentration of quenched-in vacancies.MST/826

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.346

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractIt is expected that surface treatment by CO2laser will be useful for industrial applications in which improved wear resistance is required on selected areas of already accurately machined parts. Precision in the hardening of such surfaces using laser processes is an additional advantage. Moreover, it is possible to obtain these desirable properties for low cost construction steels. The microstructural changes within the laser heated zones of commercial grade medium carbon C45 steel were determined on thin foils from the treated regions using transmission electron microscopy. Components of the substructure are described and the influence of rapid laser heating on austenite formation and its transformation into martensite are discussed.MST/563

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.350

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe scanning reference electrode technique is a recent development which enables in situ studies to be made of many forms of localised corrosion. This technique has been utilised in the design and evolution of an apparatus which can detect and monitor small potential variations associated with active pitting in FV 448 gas turbine disc steel.MST/906

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.356

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA Monte Carlo computer simulation technique, previously applied to the simulation of a number of solid state processes involving microstructural evolution, has been employed to simulate and represent pictorially grain growth and grain interactions during solidification. By careful control of the number, location, and time of origin of grain nuclei it has been possible to simulate a wide range of features of grain structure in castings. Also, in support of an existing statistical argument, it has been demonstrated that the columnar to equiaxed transition occurs when the volume fraction of equiaxed grains ahead of the columnar interface is 0·50.MST/912

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.362

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractTwo types of Co base amorphous alloy powders produced by a cavitation method were warm pressed below crystallisation temperatures. Compacts with>99% relative density were produced in an amorphous state. Compacts formed from fine powders were superior in mechanical properties, but inferior in magnetic properties to those formed from coarse powders. It was indicated by the geometry of fracture surfaces in compression tests that for amorphous compacts yield was in accordance with the von Mises criterion.MST/944

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.369

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractAn experimental apparatus to examine a bond criterion is developed. Using this apparatus, it is possible to carry out lap welding using punches that penetrate into strips of the experimental metal; these strips are simultaneously extended in the direction parallel to the bonding surface by bulging. The bond strength is investigated by varying independently the virgin surface ratioαand the normal bonding pressure p. The bond efficiencyη, i.e. the ratio of the bond strength to the strength of the base metal, increases with values ofαand p. However, when p has a value of 75 MN m−2the value ofηis always 0% at any value ofα. It is possible to commence bonding when p=112 MN m−2, a value that is nearly equal to the flow stress of the base metal Y, i.e. p/Y≍1. When p>225 MN m−2, i.e. p/Y≥2, the value ofηdoes not depend on p, but onα, i.e. bonding commences whenα=20% and the value ofηreaches 100% whenα=55–60%. This means that it is possible to achieve efficient bonding when the value of p is about twice the flow stress of the base metal, i.e. p/Y≥2.MST/889

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.4.377

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor