MatSciRN: High-Temperature Intermetallic Materials (Topic)最新文献

{"title":"The Synergistic Role of Mn and Zr/Ti in Producing Θ'/L12 Co-Precipitates in Al-Cu Alloys","authors":"J. Poplawsky, A. Shyam, L. Allard, Dongwon Shin, P. Shower, M. Chisholm","doi":"10.2139/ssrn.3547686","DOIUrl":"https://doi.org/10.2139/ssrn.3547686","url":null,"abstract":"Microstructural stability is a critical factor to consider when designing new alloys for high-temperature applications. An Al-Cu alloy with Mn and Zr additions has recently been developed to withstand extended exposures of up to 350 °C. The addition of Mn in combination with Zr and their segregation to precipitate interfaces play a significant role in stabilizing the metastable θ' precipitates responsible for the alloy's hardness; however, adding Zr and Mn separately only improves the stability to 200 °C and 300 °C, respectively. To this end, the effect of the synergistic additions on interfacial structure and chemistry was studied in detail using atom probe tomography and scanning transmission electron microscopy for Al-Cu-Mn-Zr/Ti-containing alloys subjected to long-term annealing (up to 2,100 h) in the critical temperature range, 300 °C and 350 °C, to investigate the role of Zr/Ti in increasing the θ'-precipitate stability. The results reveal how the addition of Mn allows Zr to segregate to θ' interfaces and eventually create a θ'/Al3(Zrx,Ti1-x) L12 co-precipitate structure along the interface. The co-precipitate is highly stable, as shown by density functional theory calculations, and is a key factor that governs microstructural stability beyond 300 °C. This study reveals how solute additions with different stabilization mechanisms can work in concert to stabilize a desired microstructure, the results provide insights that can be applied to other high-temperature alloy systems.","PeriodicalId":249369,"journal":{"name":"MatSciRN: High-Temperature Intermetallic Materials (Topic)","volume":"441 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129892869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Uncoupling the Effects of Strain Rate and Adiabatic Heating on Strain Induced Martensitic Phase Transformations in Steels","authors":"N. V. Fernandez, T. Nyyssönen, M. Isakov, M. Hokka, V. Kuokkala","doi":"10.2139/ssrn.3287363","DOIUrl":"https://doi.org/10.2139/ssrn.3287363","url":null,"abstract":"In this work, the effects of strain rate and adiabatic heating on the strain induced martensitic phase transformation were uncoupled and individually evaluated. Tension tests were performed at different strain rates ranging from 2x10-4 s-1 to 1400 s-1, covering both isothermal and adiabatic conditions. The adiabatic temperature rise of a sample tested at a high strain rate was replicated with heating resistors in a normally isothermal low strain rate test. This test allows studying the mechanical behavior and microstructural evolution of the material at a very low strain rate at thermal conditions similar to that of a high strain rate test. The phase transformation rates from austenite to α'-martensite were measured with the magnetic balance method. The phase transformation rate drops significantly with increasing strain rate, and the effect of adiabatic heating seems to be much smaller than the effect of strain rate. At a higher strain rate, the α'-martensite nucleates primarily on a single habit plane parallel to the primary slip plane of the parent austenite, while at a lower strain rate the α'-martensite nucleation occurs on several habit planes. At the studied plastic strains, the strain rate seems to have a stronger effect on the α'-martensite formation than the adiabatic heating. This is supported by thermodynamic stacking fault calculations, which indicate that the increase in the stacking fault energy due to adiabatic heating at low strains is small and therefore unlikely the only reason for the reduced phase transformation rate. Therefore, the strain rate itself seems to have an important role in the strain induced martensitic phase transformation rate.","PeriodicalId":249369,"journal":{"name":"MatSciRN: High-Temperature Intermetallic Materials (Topic)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128809527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Critical Thickness of High Temperature Barrier Coatings of Magnesium Oxychloride Sorrel Cement","authors":"K. Sharma","doi":"10.1115/HT2003-47392","DOIUrl":"https://doi.org/10.1115/HT2003-47392","url":null,"abstract":"The critical thickness of high temperature barrier coating is derived to avoid cycling of temperature from the finite speed heat conduction equations. When a cylinder is subject to a step change in temperature at the surface of the cylinder the transient temperature profile is obtained by the method of separation of variables. The finite speed of heat propagation is accounted for by using the modified Fourier’s law of conduction with a heat velocity of √α/τr . In order to avoid pulsations of temperature with respect to time the cylinder has to be maintained at a radius no less than 4.8096√ατr . In the asymptotic limit of infinite heat velocity the governing equation becomes parabolic diffusion equation. In the limit of zero velocity of heat and infinite relaxation time the wave equation result and solution can be obtained by a relativistic coordinate transformation. In the asymptote of zero velocity of heat and zero thermal diffusivity the solution for the dimensionless temperature is a decaying exponential in time. The average temperature of the naval warhead as indicated by UL 1709 test was estimated by using a idealized finite slab, and Leibnitz rule and an analytical expression for the average temperature was obtained using convective boundary condition. The solution is: For 1/2 >= Bi, = exp(−τ(1/2 + sqrt(1/4 − Bi*)))For Bi > 1/2, = exp(−τ/2)Cos(τsqrt(−1/4 + Bi*))) The average temperature is damped oscillatory in time domain. Further the transient temperature profile is represented by an infinite series of decaying exponential in time and Bessel function of the first kind and 0th order. The constant can be obtained from the principle of orthogonality. The bifurcated nature of the exact solution gives rise to the lower limit on the radius to avoid cycling of temperature with respect to time. The exact solution is thus, u = Σ0∝ cn J0 (λn X) exp(−τ(1/2 − sqrt(1/4 − λn2))) and when λn > 1/2 u = Σ0∝ cn J0(λn X) exp(−τ/2 Cos(τsqrt(−1/4 + λn2)) where, λn = (2.4048 + (n−1)π)(√α/τr/R) cn is given by equation (53). The term in the infinite series onward where the contribution is oscillatory is identified.Copyright © 2003 by ASME","PeriodicalId":249369,"journal":{"name":"MatSciRN: High-Temperature Intermetallic Materials (Topic)","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2003-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132444635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}