J. Poplawsky, A. Shyam, L. Allard, Dongwon Shin, P. Shower, M. Chisholm
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.
{"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}
N. V. Fernandez, T. Nyyssönen, M. Isakov, M. Hokka, V. Kuokkala
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.
{"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}
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