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951.
G-phase precipitation in the ferrite phase in thermally aged duplex stainless steel (DSS) was investigated. A needle-shaped sample of DSS aged at 673?K for 5000?h was observed by transmission electron microscopy (TEM), and subsequently by atom probe tomography (APT). The precipitates of the G-phase observed by TEM corresponded well to clustering atoms observed by APT. On the other hand, regarding the precipitates of the G-phase that formed in an earlier stage of aging, the present study suggests that not all the precipitates can be detected by TEM. A large area of DSS aged at 673?K for 5000?h containing both the ferrite and austenite phases was observed. The number density of precipitates of the G-phase in the ferrite phase was small in the vicinity of the phase boundary and increased with the distance between the phase boundary and each field of view. The number density reached an almost constant value at a distance of approximately 4?µm from the phase boundary. The suppression of G-phase precipitation in the vicinity of the phase boundary is discussed in terms of the depletion of alloying elements that comprise the G-phase. 相似文献
952.
AbstractGrain boundary engineering has revealed significant enhancement of material properties by modifying the populations and connectivity of different types of grain boundaries within the polycrystals. The character and connectivity of grain boundaries in polycrystalline microstructures control the corrosion and mechanical behaviour of materials. A comprehensive review of the previous researches has been carried out to understand this philosophy. Present research thoroughly explores the effect of total strain amplitude on phase transformation, fatigue fracture features, grain size, annealing twinning, different grain connectivity and grain boundary network after strain controlled low cycle fatigue deformation of austenitic stainless steel under ambient temperature. Electron backscatter diffraction technique has been used extensively to investigate the grain boundary characteristics and morphologies. The nominal variation of strain amplitude through cyclic plastic deformation is quantitatively demonstrated completely in connection with the grain boundary microstructure and fractographic features to reveal the mechanism of fatigue fracture of polycrystalline austenite. The extent of boundary modifications has been found to be a function of the number of applied loading cycles and strain amplitudes. It is also investigated that cyclic plasticity induced martensitic transformation strongly influences grain boundary characteristics and modifications of the material’s microstructure/microtexture as a function of strain amplitudes. The experimental results presented here suggest a path to grain boundary engineering during fatigue fracture of austenite polycrystals. 相似文献
953.
954.
D. L. Damcott J. M. Cookson R. D. Carter JR. J. R. Martin M. Atzmon G. S. Was 《辐射效应与固体损伤》2013,168(4):383-392
Abstract A technique is developed which addresses the problem of irradiation assisted stress corrosion cracking of stainless steels in light water reactors using high energy protons to induce grain boundary segregation. These results represent the first grain boundary segregation measurements in bulk produced by proton irradiation of stainless steel. The technique allows the study of grain boundary composition with negligible sample activation, short irradiation time, rapid sample turnaround and at minimal cost. Scanning Auger electron microscopy is used to obtain grain boundary composition measurements of irradiated and unirradiated samples of ultra high purity (UHP) type 304L stainless steel and UHP type 304L steels with the additions of phosphorus (UHP + P) and sulphur (UHP + S). Results show that irradiation of all three alloys causes significant Ni segregation to the grain boundary and Cr and Fe away from it. Irradiation of the UHP + P alloy also results in segregation of P at the grain boundary from 5.3 to 8.7 at %, over 80 times the bulk value. No radiation-induced grain boundary segregation of S was measured in the UHP + S alloy. Results also indicate that the presence of P or S may enhance radiation-induced segregation of major alloying elements at the boundary. Comparison of irradiated and unirradiated regions of the UHP + P alloy indicate that while a prior thermal treatment segregates P to the grain boundary to 5.3 at %, the major element concentrations at the grain boundary are completely different from those under irradiation. 相似文献
955.
激光表面织构化对GCr15钢摩擦磨损性能的影响 总被引:12,自引:7,他引:5
本文利用Nd:YAG固体脉冲激光对GCr15钢样品表面进行了微坑织构化处理,考察了激光表面织构参数对其摩擦性能的影响,同时通过扫描电镜等对磨斑表面进行了分析.结果表明:与光滑面试样相比,经织构化处理的样品表面在干摩擦条件下虽然摩擦系数较高,但表现出了较好的抗磨性能;在贫油润滑条件下,织构面的摩擦系数与磨损均明显小于光滑面;在低载低速下较小孔径织构面摩擦系数较小,随着速度及载荷的增大,较大孔径织构面表现出更好的摩擦学性能.采用Stribeck曲线探讨了织构化表面与光滑面在贫油润滑下的润滑机理,结果表明织构面在试验条件下均保持油膜流体润滑状态. 相似文献
956.
研究了低合金热轧钢16MnR缺口试样在$-196\,{^\circ}$C和$-130\,{^\circ}$C的解理断裂机
理. 拉伸试验、单、双缺口四点弯曲实验、断口形貌观察以及有限元分析结果表明, 缺口试
样发生解理断裂时均起裂于夹杂物粒子, 一种位于缺口根部前端(IC型), 另一种位于距缺口
根部较远的条形裂纹前端(SIC型); 且随温度升高, 起裂源的类型从$-196\,{^\circ}$C下的IC
型转变为$-130\,{^\circ}$C下的SIC型. 微裂纹均形核于夹杂物, 最终的断裂由铁素体晶粒尺
寸的微裂纹扩展控制. 缺口试样IC型解理断裂遵循裂纹形核条
件$\varepsilon_{\rm p}
\ge \varepsilon_{\rm pc}$和裂纹扩展条件$\sigma_{yy}
\ge \sigma_{f}$, 而SIC型解理断裂条件则演化为$\varepsilon_{\rm p}+\varepsilon_{\rm ps}
\ge \varepsilon_{\rm pc}$和$\sigma_{yy} +\sigma_{yy{\rm s}} \ge \sigma_{f}$. 相似文献
957.
958.
An extended version of Hatzopoulos and Haberman (2009) dynamic parametric model is proposed for analyzing mortality structures, incorporating the cohort effect. A one-factor parameterized exponential polynomial in age effects within the generalized linear models (GLM) framework is used. Sparse principal component analysis (SPCA) is then applied to time-dependent GLM parameter estimates and provides (marginal) estimates for a two-factor principal component (PC) approach structure. Modeling the two-factor residuals in the same way, in age-cohort effects, provides estimates for the (conditional) three-factor age-period-cohort model. The age-time and cohort related components are extrapolated using dynamic linear regression (DLR) models. An application is presented for England & Wales males (1841-2006). 相似文献
959.
Julien MostardRuud Teunter René de Koster 《European Journal of Operational Research》2011,211(1):139-147
The problem considered is that of forecasting demand for single-period products before the period starts. We study this problem for the case of a mail order apparel company that needs to order its products pre-season. The lack of historical demand data implies that other sources of data are needed. Advance order data can be obtained by allowing a selected group of customers to pre-order at a discount from a preview catalogue. Judgments can be obtained from purchase managers or other company experts. In this paper, we compare several existing and new forecasting methods for both sources of data. The methods are generic and can be used in any single-period problem in the apparel or fashion industries. Among the pre-order based methods, a novel ‘top-flop’ approach provides promising results. For a small group of products from the case company, expert judgment methods perform better than the methods based on advance demand information. The comparative results are obviously restricted to the specific case study, and additional testing is required to determine whether they are valid in general. 相似文献
960.