摘要:

AbstractTensar polymer grids (geogrids) are oriented integral polyolefin structures, specifically developed to reinforce and stabilize soil in civil engineering works for which there is a design life of 100 years or more for buried materials. It is confirmed, from the results of work by others, that their composition and structure give these geogrids good resistance to biological attack and detrimental aging in such applications. Environmental stress cracking and outdoor weathering are discussed in detail, and results of specially commissioned tests in both areas are presented. Methods used to establish a 120-year load-bearing capacity are explained. It is seen that currently the performance of a structure reinforced by Tensar geogrids is determined by soil strain, not reinforcement strength. Any damage that may be caused to the geogrids must be taken into account at the design stage. Large-scale tests carried out to determine the magnitude of such damage are described, and the results presented.MST/591

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.161

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractElements of groups IA and IIA form many compounds with elements of the third long period passing back from bismuth to platinum; fewer compounds are formed with elements of the second and earlier periods. The incidence of such compounds has been analysed graphically such that the valencies on the components may be inferred. The compounds exhibit low valency on the second/third long period component, and normal valency on the A-element. The compounds are covalent in character, and are formed across the ionic divide consistent with Fajans' rule.MST/464

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.171

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA crystal structure of theT1phase (Al2CuLi), commonly observed in aged Al–Cu–Li alloys containing ~3%Cu and 2%Li, is proposed. It is an‘ideal’crystal structure in the sense that it predicts X-ray peaks with intensities in fair agreement with those reported semiquantitatively by Hardy and Silcock, but for which additional structure refinement is not warranted. With the ideal crystal structure as a basis, the expected electron diffraction patterns for the zone axes [00l], [110], [111], [112], [013], and [114]have been predicted. These are demonstrated to be in excellent agreement with those observed experimentally. However, in addition to the structure factor for the unit cell, multiple diffraction, theT1plate thickness and shape, the number ofT1variants contributing to a given reflection, and possibly faulting within theT1particles all contribute to the intensities of the diffracted electron beams. The roles of plate thickness and multiple diffraction are particularly important since many of theT1reflections observed are not centred onT1reciprocal lattice points lying exactly in the zero order Laue zone of the matrix. The observedT1reflections are therefore frequently a consequence of the intersections of streaks of diffracted intensity with the reflecting sphere. Since all the observed diffraction effects are attributable toT1precipitates there is no need to invoke the existence of a precursorT1′phase, as has been recently proposed. It is concluded that there is no evidence for the existence of a metastable plate-shaped precipitate precedingT1particles in the aging sequence of the alloy.MST/599

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.176

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractTo optimize the properties of the new corrosion resisting steel 3CR12 the microstructure has been studied as a function heat treatment. The kinetics of both the decomposition of austenite and the reaustenization reactions have been investigated using a series of isothermal anneals. The steel has a dual phase ferrite–austenite structure between 800 and 1350°C and the amount of austenite is maximum at about 1050°C. At this temperature a higher nickel version of the alloy is fully austenite. On cooling to ambient temperature, the austenite transforms to a lath-type martensite. Heat treatments at temperatures up to 800°C cause the slow tempering of the martensite, the recovery and recrystallization of original ferrite regions, and the nucleation and growth of newly formed ferrite. The growth of ferrite requires the concomitant precipitation of carbides and nitride particles from the austenite or martensite and these particles mark the stepwise movement of the interface. In contrast the reaustenization does not require any immediate redistribution of elements. Consequently, the hardness of the resulting martensite is a function of both the temperature and time of the austenization treatment. These findings can be used to advantage by the producers, fabricators, and end users of the steel since variations in thermomechanical treatments promote differences in formability, strength, and toughness.MST/493

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.189

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractNucleation theory and the solubility product of niobium, carbon, and nitrogen in austenite have been used to derive equations for the start of Nb (C, N) precipitation as a function of temperature and composition. The predicted curves have been compared with the experimental observations of several authors to determine the effects of thermomechanical processing variables on the density of preferred nucleation sites and to incorporate these in the equations. Good agreement between the predicted and observed forms of precipitation curve is obtained with consistent constants in the equations when account is taken of the influence of different methods of detecting the onset of precipitation. Combining the calculated precipitation start curves with the dependence of recrystallization kinetics on composition and thermomechanical process variables when all niobium is in solution leads to prediction of the lower temperature limit for complete recrystallization and of the upper temperature limit for effective stoppage of recrystallization by precipitation. The predictions are in good agreement with observed results.MST/495

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.197

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractVacuum melted electrolytic iron and alloys of Fe–P, Fe–Mn, Fe–Cr, Fe–Mn–P, and Fe–Cr–P were employed in a study of the effects of chromium and manganese on phosphorus segregation and intergranular embrittlement. The effects of carbon were examined by hydrogen-decarburization of the original low carbon (10–60 ppm) alloys. The critical fracture stress was measured by pure bending of notched bars at 133 K, and the grain boundary compositions were measured by Auger electron spectroscopy. Manganese was found to segregate in the absence of phosphorus and to be a powerful embrittling element. Carbon was found to exert a great intergranular strengthening effect. It also interfered with the segregation of phosphorus; the latter effect was reduced by the presence of chromium, in agreement with the prior report of Erhart and Grabke. In decarburized alloys the presence of manganese caused increased phosphorus segregation but not when carbon was present at 10–30 ppm. Segregation of manganese and chromium were both increased by the presence of phosphorus.MST/500

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.207

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractStress intensity levels at the tip of cracks approaching and growing past second-phase particles have been computed using finite element methods. It is predicted that particles having a lower modulus than the matrix (i.e.‘soft’particles) attract and accelerate cracks growing into their vicinity, whereas‘hard’particles deflect them and retard local growth. A reverse, but weaker, effect is indicated once the crack has extended past a particle. Using a ferrite matrix with either spheroidized cementite or spheroidal graphite as the second phase, these predictions have been largely verified experimentally. An apparent anomaly is the cross-over in the growth rate curves of the cast iron and the totally ferritic microstructure. However, this may be explained by the requirement for the crack to reinitiate following its interaction with each graphite particle, during which decohesion of the particle/matrix interface occurs.MST/417

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.217

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA procedure was demonstrated for predicting the effect of upward temperature excursions on the long-term creep of a type 316 steel. The procedure exploits the existence of regimes of stable creep at 600–750°C, from which creep rates can be used to predict long-term strain accumulation or rupture, without the problems associated with the history dependence of creep rupture data for solution treated steel. Pre-aging can be used to remove the potential for transient metallurgical strengthening and ensure stable creep. The excursion tests were run under the relevant conditions and the overall creep rate determined for a few cycles, for comparison with isothermal behaviour. Creep strains caused by the 1 h excursions were consistent with stable creep at the excursion temperature. Thus, the transient increased strain rate observed after excursions must have been compensated by a transient depression of strain rate on reaching the excursion temperature.MST/580

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.224

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe structure and properties of electroless nickel are highly sensitive to heat treatment owing to its pronounced metastability. The heat treatment process induces crystallization of amorphous nickel to nickel phosphides and fcc nickel by a mechanism similar to that of the solidification of liquid alloys. The process produces a twofold increase in hardness, the elimination of severe adhesive wear, and a deterioration in the abrasive scratch resistance. The susceptibility of the as deposited coating to severe adhesive wear during unlubricated sliding against plain carbon steel is due to the low interfacial and high surface free energies of the two surfaces, resulting in a high compatibility. Heat treatment removes severe wear by changing the structure from amorphous nickel to Ni3P, which presents a surface incompatible to steel. The abrasive scratch resistance of the as-deposited coating is a result of its relatively high fracture toughness, which is attributable to the absence of heterogeneities in the amorphous structure. The relevance of the data to engineering applications is discussed.MST/539

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.3.228

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor