首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
Microplasticity in Elgiloy   总被引:2,自引:0,他引:2  
The room temperature microstrain characteristics of Elgiloy (composition in wt%, 40 Co, 20 Cr, 15 Ni, 7 Mo, 2 Mn, 0.1 C, balance Fe) have been determined for a range of microstructures corresponding to various alloy treatments reported previously. The friction stress was found to be constant ( F=12±3 MN m–2) for the solution treated (after prestrain), cold-worked and cold-worked plus aged at 500° C conditions, but decreased to f=5±3 MN m–2 after ageing at 800° C. The microscopic yield stress (MYS) increased with cold-working and subsequent ageing at 500° C to a maximum value of 210 MN m–2 reflecting the increase in the long range internal stress field. An increase in the MYS of the solution treated strip was noted with ageing at 800° C, whereas the MYS of the cold-worked samples was decreased by this treatment. The solution treated and aged at 800° C samples exhibited a two-stage stress-plastic microstrain curve, whereas the cold-worked and cold-worked plus aged at 500° C conditions showed a three-stage stress-plastic microstrain behaviour.  相似文献   

2.
Metals can be strengthened by methods appropriately combined to meet the operating conditions. In this ‘alloy design’, effort, we are guided by semi-quantitative relations that have been developed over the years and which relate the efficacy of the strengthening methods to the deformation modes. In this paper, the basic concepts are expanded with specific reference to dislocation glide, diffusional creep, grain boundary sliding and high strain rate deformation.  相似文献   

3.
Abstract

The mechanisms responsible for strengthening a series of high-strength cold-rolled steels with tensile strengths up to 800 MN m?2 have been investigated. The magnitude of precipitation strengthening in the annealed steels is shown to be in agreement with the Orowan-Ashby model for non-deforming particles. Strengthening depends only upon the volume fraction and diameter of the precipitates, and is not influenced by their chemical composition, nor by whether the precipitation-hardening elements are added singly or in combination. Manganese alone is a weak solid-solution-strengthening agent, but has a synergistic effect in combination with titanium or niobium, which is attributed to its depression of the austenite-ferrite transformation and precipitation temperatures. Vanadium is a much less efficient strengthening element than titanium or niobium in annealed steel, owing to the rapid coarsening rate of vanadium carbonitride precipitates and the considerable loss in strength on processing from hot-rolled coil to annealed sheet. Sulphur acts to reduce the strength of the annealed steels and tends to coarsen the grain structure. The physical basis of this effect is not known, but it is suggested that it may be associated with the partial solution of managanese sulphide during slab reheating and its subsequent re-precipitation during hot rolling. Phosphorus and nitrogen are the most efficient strengthening agents up to tensile strengths of 450 MN m?2, but stronger materials require a combination of strengthening modes, depending upon the application.

MST/111  相似文献   

4.
Silicon carbide whisker reinforced aluminium alloys were mechanically tested in the as-cast and heat treated conditions; the microstructures were examined by transmission electron microscopy. The mechanical properties were strongly dependent upon the nature of the matrix alloying elements, the heat treatment conditions and the processing routes. Al-Cu and Al 6061 reinforced alloys were very responsive to heat treatment while Al-Mg and Al-Si reinforced alloys were not. The microstructures and mechanical properties were analysed in an attempt to determine the operative strengthening mechanisms and deformation processes. Three distinct types of matrix microstructure were observed, distinguished by the presence or absence of subgrains and/or precipitates. Using these observations, the composite properties could be quite well modelled using dislocation theories, indicating that the matrix microstructure dominates the mechanical properties.  相似文献   

5.
Understanding the main relationships between the microstructure parameters controlling the strength and ductility of low temperature bainitic microstructures is of considerable importance for further development of these grades. Although the microstructure essentially consists of solely two phases, bainitic ferrite and retained austenite, the complexity of the different microstructural characteristics, the natural consequence of its unique transformation mechanisms, might not provide with one unique answer, but a set of several parameters interdependent among them. This paper will deal with some of these relationships’ microstructure properties, strength, and ductility, with special emphasis in the mechanical stability (TRIP effect) of retained austenite.  相似文献   

6.
Materials with quasi-brittle stress strain curves exhibit desirable properties such as enhanced durability, flaw tolerance and toughness. This study reveals that steel microfiber reinforced cement based composites exhibit such quasi-brittle behavior. Mechanical properties of steel microfiber reinforced cement based composites are obtained through flexure and splitting tension tests. The cracking process and crack fiber interactions that lead to the quasi-brittle behavior in these composites were investigated. The strength and toughness enhancement is associated with crack wake mechanisms. Aggregate bridging and pullout and secondary crack formations associated with microfiber bridging sites are predominant during the strain hardening regime. Multiple secondary microcracks perpendicular to the fiber/matrix interface is the dominant failure mode beyond peak load in the strain softening regime.  相似文献   

7.
Journal of Materials Science - Nanoporous metallic foams (NMFs) of Cu, Cu–Zn, and Cu–Ni alloys with relative densities between 0.5 and 14% were created by polymer templating followed by...  相似文献   

8.
Strengthening mechanisms in a rapidly solidified and aged Cu-Cr alloy   总被引:8,自引:0,他引:8  
A single-roller melt spinning method was used to produce Cu-Cr microcrystal alloy ribbons. Upon proper aging treatment, the strength and hardness of the alloy were remarkably enhanced while the conductivity only had a minimal decrease. Grain refinement and coherent dispersion strengthening were proved to be the major factors contributing to the improvement of strength and hardness of the alloy after aging. The degree of coherent strengthening was almost identical with that calculated by the Gerold equation. Compared with the solid solution quenched Cu-Cr alloy, the peak hardness was increased 2.6 times, in which about 27% was attributed to the grain refinement and 73%, in turn, provided by coherent strengthening due to aging precipitation. Neither the solid solution strengthening nor vacancy strengthening had detectable effect on the strength and hardness of the rapidly solidified Cu-Cr alloy.  相似文献   

9.
10.
This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium (Y) element. The addition of Y resulted in the formation of ternary I (Mg3YZn6), W (Mg3Y2Zn3) and LPSO (Mg12YZn) phases which subsequently reinforced alloys ZM31 + 0.3Y, ZM31 + 3.2Y and ZM31 + 6Y, where the value denoted the amount of Y element (in wt%). Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion (CTE), which was derived to be 1.38 × 10?5 K?1 and 2.35 × 10?5 K?1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and CTE mismatch were the predominant strengthening mechanisms in the ZM31 + 0.3Y and ZM31 + 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 + 6Y alloy.  相似文献   

11.
ABSTRACT

This paper reports the microstructure evolution, mechanical properties and strengthening mechanisms of a commercial purity Al alloy (Al 1350) after severe plastic deformation by a novel continuous method called ‘Equal Channel Angular Torsion Drawing (ECATD)’. Electron backscatter diffraction (EBSD) results revealed an inhomogeneous grain refinement including a large fraction of low-angle grain boundaries. After four passes, the microhardness increases from the initial value of 35?HV up to 44 and 62?HV at the centre and near to wire surface, respectively. A combination of high strength and ductility can be achieved based on the results of a Taguchi design of experiment (DoE) for mechanical properties. The strengthening occurs due to increment of the dislocation density, and development of mainly new low-angle grain boundaries.  相似文献   

12.
A strengthening mechanism merely arising from internal (residual) microstresses due to thermal expansion mismatch is proposed for explaining the high experimental strength data measured in Al2O3/SiC nanocomposites. Upon cooling, transgranular SiC particles undergo lower shrinkage as compared to the surrounding matrix and provide a hydrostatic “expansion” effect in the core of each Al2O3 grain. Such a grain expansion tightens the internal Al2O3 grain boundaries, thus shielding both weakly bonded and unbonded (cracked) grain boundaries. It is shown that the shielding effect by intragranular SiC particles is more pronounced than the grain-boundary opening effect eventually associated with thermal expansion anisotropy of the Al2O3 grains, even in the “worst” Al2O3-grain cluster configuration. Therefore, an improvement of the material strength can be found. However, a large stress intensification at the grain boundary is found when intergranular SiC particles are present, which can produce a noticeable wedge-like opening effect and trigger grain-boundary fracture. The present model enables us to explain the experimental strength data reported for Al2O3/SiC nanocomposites and confirms that the high strength of these materials can be explained without invoking any toughening contribution by the SiC dispersion.  相似文献   

13.
ABSTRACT

A friction stir processing (FSP) method has been developed to fabricate a locally reinforced aluminum matrix composite (AMC) by stirring electroless-copper-coated SiC particles into AA6061 matrix. The interfacial bonding between particulate reinforcement and the matrix was enhanced by the copper coating. Effective improvement in hardness and in tensile strengths has been proved. Microstructural investigation and analyses were conducted to correlate the microstructural evidences with the possible strengthening mechanisms. The effect of copper coating on the bonding between SiC particles and Al-matrix; the role of the dispersed Cu debris and the increased Cu content in solid solution on the strengthening; and the effect of friction stir on dislocation density and on the recrystallization behavior were analyzed. Multiple strengthening mechanisms due to diffusion between copper film and matrix; dispersion of fine copper debris and Al-Cu intermetallic compounds (IMCs) in the matrix; solid solution due to increased copper content and dislocation punching were four major mechanisms in interpreting the strengthening phenomena in AMC containing copper coated SiC reinforcements.  相似文献   

14.
蓝宝石窗罩在气动热效应作用下易产生破裂,使其结构/功能失效.提高蓝宝石高温强度可有效抑制其高温断裂行为.结合国内外研究成果,从蓝宝石高温失效机理、蓝宝石高温强度表征新方法和蓝宝石强化方法等方面,综合评述了蓝宝石强化研究领域的最新成果,其中重点介绍了蓝宝石强化的研究进展,最后指出了我国蓝宝石强化研究的努力方向.  相似文献   

15.
M. L. Bhatia 《Sadhana》1980,3(4):297-313
Strengthening alloys against creep deformation involves strengthening against dislocation glide and climb, and grain-boundary sliding. The rationale behind various techniques currently used for strengthening are discussed, especially with reference to Ni-base superalloys. Although one should try and minimize sliding by increasing grain-boundary viscosity, the grains should not be over-strengthened to minimize problems due to creep cavitation.  相似文献   

16.
17.
Lightweight cellular concretes are attractive building materials for a number of reasons: they offer a unique combination of moderate thermal insulation and stiffness, low cost and incombustibility. They have relatively low strength, however, and are brittle. In this paper we describe the behaviour of composite cement/polystyrene foams with improved strength and ductility.  相似文献   

18.
招贴艺术具备了视觉语言中大多数基本要素,设计表现比其他媒体更广、更全面.要想取得招贴诉求的最佳效果,视觉冲击力度的强弱是关键.文章在分析招贴的发展历史及传播特性的基础上,针对招贴设计中视觉冲击力的强化问题,从图形识剐、版式引导、色彩注目、感官刺激、加深记忆、心理震撼等6个方面,进行了创意策略分析及设计方法的分类研究与探索.  相似文献   

19.
Strengthening in magnesium alloys by icosahedral phase   总被引:1,自引:0,他引:1  
Strengthening effects of quasicrystalline icosahedral phase has been studied in two alloys Mg95Zn4.2Y0.8 and Mg92.5Zn6.5Y extruded at 250 and 400 °C. The quasicrystal particles are facetted and show definite orientation relationships with the matrix. Due to its high symmetry and quasiperiodicity, the icosahedral phase can form strong interfaces with the matrix in various orientations. The icosahedral phase particles have a strong pinning effect on the grain boundaries, which stabilizes grain size. The icosahedral particles are resistant to coarsening, and remain hard at higher temperatures, imparting good strength with ductility at 200 °C. Very few deformation structures such as high dislocation density and twins are observed after extrusion or tensile tests. Dislocations commonly observed are c-type. Due to the stability of microstructure, various post-extrusion treatments are possible. In the Mg92.5Zn6.5Y alloy upon annealing at 400 °C the icosahedral phase transforms to a hexagonal Mg25Zn58Y17 phase. The icosahedral phase then reprecipitates on its interface, forming a nano-composite. Effects of microstructural features on the deformation behavior are described.  相似文献   

20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号