Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_...Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_(22)Co_(26)Cr_(20)Ni_(22)Ta_(10)−(BaF_(2)/CaF_(2))x(x=3−20,wt.%)composites were prepared by spark plasma sintering(SPS),with BaF_(2)/CaF_(2) eutectic powder used as solid lubricant.The lubrication behavior and mechanical properties were studied at both room and high temperatures.With the increase of the content of BaF_(2)/CaF_(2) eutectic powder,the friction coefficients and the wear rates of the composites at 600 and 800℃ decrease significantly.The composites with eutectic powder content of 15 and 20 wt.%have the best lubricating performance at 600℃,with low friction coefficient and wear rates,mainly due to the good mechanical properties of EHEA matrix,the lubrication effect of BaF_(2)/CaF_(2) phase and the oxides formed on the worn surface.展开更多
A high-quality 1%(atom fraction)Ho^(3+):BaF_(2) crystal was successfully grown using the temperature gradient technique(TGT).The optical properties of the crystal were investigated,and continuous-wave(CW)laser operati...A high-quality 1%(atom fraction)Ho^(3+):BaF_(2) crystal was successfully grown using the temperature gradient technique(TGT).The optical properties of the crystal were investigated,and continuous-wave(CW)laser operation of Ho^(3+)ions in the 2μm range was successfully demonstrated for the first time in the BaF_(2) crystal,to the best of our knowledge.Spectral parameters such asΩ_t(t=2,4,6)and radiative lifetimes were calculated and studied by the Judd-Ofelt(J-O)theory.The quality factor was calculated to be Q=6.60×10^(-20)cm^(2)·ms,and the full width at half-maximum(FWHM)was fitted to be 134.5 nm,indicating that the Ho:BaF_(2) crystal has a low laser threshold and broadband tunability.A maximum output power of 1.5 W and a slope efficiency of 29.3%were achieved by the 1908 nm fiber laser as the pumping source,with a relatively low threshold of 399 mW.Additionally,the Ho:BaF_(2) crystal achieved a tunable laser output with a bandwidth of 166.4 nm,which is the widest as reported for other 2μm band Ho-doped fluoride crystals to the best of our knowledge.These results suggest that the Ho:BaF_(2) crystal has the potential to achieve femtosecond ultrafast pulse laser output through mode-locking operation.展开更多
基金The authors acknowledge the financial support from the National Natural Science Foundation of China(51671217).
文摘Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_(22)Co_(26)Cr_(20)Ni_(22)Ta_(10)−(BaF_(2)/CaF_(2))x(x=3−20,wt.%)composites were prepared by spark plasma sintering(SPS),with BaF_(2)/CaF_(2) eutectic powder used as solid lubricant.The lubrication behavior and mechanical properties were studied at both room and high temperatures.With the increase of the content of BaF_(2)/CaF_(2) eutectic powder,the friction coefficients and the wear rates of the composites at 600 and 800℃ decrease significantly.The composites with eutectic powder content of 15 and 20 wt.%have the best lubricating performance at 600℃,with low friction coefficient and wear rates,mainly due to the good mechanical properties of EHEA matrix,the lubrication effect of BaF_(2)/CaF_(2) phase and the oxides formed on the worn surface.
基金supported by the National Key Research and Development Program of China(Nos.2022YFB3605701 and 2023YFB3507401)the National Natural Science Foundation of China(Nos.62275198 and 52032009)。
文摘A high-quality 1%(atom fraction)Ho^(3+):BaF_(2) crystal was successfully grown using the temperature gradient technique(TGT).The optical properties of the crystal were investigated,and continuous-wave(CW)laser operation of Ho^(3+)ions in the 2μm range was successfully demonstrated for the first time in the BaF_(2) crystal,to the best of our knowledge.Spectral parameters such asΩ_t(t=2,4,6)and radiative lifetimes were calculated and studied by the Judd-Ofelt(J-O)theory.The quality factor was calculated to be Q=6.60×10^(-20)cm^(2)·ms,and the full width at half-maximum(FWHM)was fitted to be 134.5 nm,indicating that the Ho:BaF_(2) crystal has a low laser threshold and broadband tunability.A maximum output power of 1.5 W and a slope efficiency of 29.3%were achieved by the 1908 nm fiber laser as the pumping source,with a relatively low threshold of 399 mW.Additionally,the Ho:BaF_(2) crystal achieved a tunable laser output with a bandwidth of 166.4 nm,which is the widest as reported for other 2μm band Ho-doped fluoride crystals to the best of our knowledge.These results suggest that the Ho:BaF_(2) crystal has the potential to achieve femtosecond ultrafast pulse laser output through mode-locking operation.
