New non-equiatomic Ti_(25+x)-Zr₂₅-Nb₂₅-Ta_(25-x) (x = 0, 5, 10, 15, 20, in at%) medium entropy alloys (MEAs) have been designed using the atomic mismatch approach and fabricated through a conventional arc-melting process. These novel MEAs were derived from a recently developed equiatomic Ti-Zr-Nb-Ta MEA by gradually replacing its Ta content with Ti. Each non-equiatomic MEA solidified as a single solid-solution phase, which was characterised in detail and compared with Pandat™ simulation and empirical rules. Systematic tensile mechanical property data revealed the existence of a brittle-to-ductile transition for Ti-Zr-Nb-Ta MEAs, i.e., when 15 at% of Ta in the equiatomic Ti₂₅-Zr₂₅-Nb₂₅-Ta₂₅ MEA was replaced by Ti to become a Ti₄₀-Zr₂₅-Nb₂₅-Ta₁₀ MEA. The transition occurs corresponding to a small reduction in atomic mismatch from 4.72% to 4.65% but a signficant drop in nanoindentation hardness from 4.2 GPa to 3.5 GPa. In particular, both the as-cast Ti₄₀-Zr₂₅-Nb₂₅-Ta₁₀ and Ti₄₅-Zr₂₅-Nb₂₅-Ta₅ MEAs exhibited excellent tensile strain to fracture (>18%) and tensile strength (>900 MPa) with much reduced density compared to the brittle Ti₂₅-Zr₂₅-Nb₂₅-Ta₂₅ MEA. They are both among a very small number of strong and ductile (tensile strain >15%) HEAs reported to date. Their tensile mechanical properties can be further tuned by adjusting the atomic mismatch of the resulting single solid-solution phase in conjunction with the improved understanding of the microstructures of these MEAs.

已经使用以下方法设计了新的非等原子Ti _{（25 + x）} -Zr ₂₅ -Nb ₂₅ -Ta _（25-x）（x = 0、5、10、15、20 ，at％）原子失配方法，并通过传统的电弧熔化工艺制造。这些新颖的MEA源自最近开发的等原子Ti-Zr-Nb-Ta MEA，通过逐步将其Ta含量替换为Ti来实现。每个非等原子MEA都固化为单个固溶体相，对其进行了详细表征，并与Pandat™模拟和经验规则进行了比较。系统的拉伸力学性能数据表明，Ti-Zr-Nb-Ta MEAs存在脆性-延性转变，即当等原子Ti ₂₅ -Zr ₂₅ -Nb中Ta的含量为15 at％时用Ti代替₂₅ -Ta ₂₅ MEA成为Ti ₄₀ -Zr ₂₅ -Nb ₂₅ -Ta ₁₀ MEA。发生转变的原因是原子错配从4.72％降低到4.65％，但纳米压痕硬度从4.2 GPa显着下降到3.5 GPa。尤其是铸态的Ti ₄₀ -Zr ₂₅ -Nb ₂₅ -Ta ₁₀和Ti ₄₅ -Zr ₂₅ -Nb ₂₅ -Ta ₅ MEA均表现出优异的断裂拉伸应变（> 18％）和拉伸强度（> 900 MPa） ）与脆性Ti ₂₅ -Zr相比密度大大降低₂₅ -Nb ₂₅ -Ta ₂₅ MEA。迄今为止，它们都属于极少数的强而有延展性（拉伸应变> 15％）的HEA。通过调节所得单固溶相的原子错配以及对这些MEA微观结构的更好理解，可以进一步调节其拉伸机械性能。