以小角度X光散射技術探討合金早期析出行為之研究

Abstract

本研究利用小角度X光散射(SAXS)技術探討在Ti48.7Ni51.3形狀記憶合金中富鎳奈米域和Ti3Ni4奈米析出物於250°C時效下之演進及熱循環中之應變玻璃轉變、Mg-10.54 Li-1.11 Al-0.38 Zn (LAZ1110)合金中θ-MgLi2Al析出物在早期自然時效下之演進，以及冷軋延的等原子比CoCrFeMnNi高熵合金中奈米析出物於350–500 °C時效和Al0.2CoCrFeMnNi高熵合金中GP zone於550 °C時效之成長動力學，並針對析出物其相對體積分率、尺寸和形貌進行後續討論。Ti48.7Ni51.3應變玻璃之富鎳奈米域於淬火過程中就產生，隨著250°C時效而漸漸溶解，同時Ti3Ni4奈米析出物隨之成核、成長和粗化。其中，奈米域的鎳原子分佈為核殼結構，並由富鎳殼和高富鎳核組成。當MgLiAlZn合金固溶處理後自然時效，θ析出物之半徑從3.1奈米漸漸成長至6.9奈米，而其厚度則依然維持在約3.7奈米。θ析出物之相對體積分率在時效早期先快速上升接著趨緩，析出物成長至約17小時後達到峰值並擁有最高的硬度。而在冷軋延CoCrFeMnNi合金中之奈米析出物經500°C時效，其尺寸從原先半徑約1.2奈米之球狀析出物快速成長，並於時效60分鐘時達到析出飽和。冷軋延Al0.2CoCrFeNi合金中的雙峰時效硬化歸因於兩組GP zone的貢獻。DSC和XRD的實驗結果也顯示合金中之析出物的相演進。TEM觀察也呈現出析出物的尺寸和形貌，用以和SAXS結果相對照。最後，相關的機械性質也藉由DMA、硬度和拉伸試驗來和SAXS結果相互連結，包含應變玻璃的轉換特性、顯著的析出硬化效應等。

Small-angle X-ray scattering (SAXS) was used to reveal the evolutions of Ni-rich nanodomains and Ti3Ni4 nanoprecipitates in the Ti48.7Ni51.3 shape memory alloy aged isothermally at 250 °C and the strain glass transition in as-quenched Ti48.7Ni51.3 shape memory alloy during a thermal cycle, the evolution of the θ-MgLi2Al precipitates in the early aging stage at room temperature in the Mg-10.54 Li-1.11 Al-0.38 Zn (in wt.%) (LAZ1110) magnesium alloy, and the growth kinetics of nanoprecipitates of cold-rolled equiatomic CoCrFeMnNi high-entropy alloy aged at 350–500 ºC and Al0.2CoCrFeNi high-entropy alloy aged at 550 °C in terms of relative volume fraction, radius, thickness, and morphology. Ni-rich nanodomains in the Ti48.7Ni51.3 strain glass are formed in the quenching process and dissolve while Ti3Ni4 nanoprecipitates nucleate, grow and coarsen during aging. The distribution of Ni atoms in nanodomains is identified as a disk-like core–shell configuration with a Ni-rich shell and a highly Ni-rich core. The radius of θ precipitates in the MgLiAlZn alloy grows gradually from 3.1 nm to 6.9 nm with a nearly constant thickness of 3.7 nm. The relative volume fraction of θ precipitates increases rapidly in the early aging stage and then more slowly in the peak aging stage at ~17 hrs. The nanoprecipitates in the cold-rolled CoCrFeMnNi high-entropy alloy have a radius of ~1.2 nm, grow drastically in the early 30 min of aging at 500 ºC, and reach the saturation stage at 60 min aging. The double-peaked aging behavior exhibited in cold-rolled Al0.2CoCrFeNi high-entropy alloy is attributed by the contribution of the two groups of GP zones divided into GP1 and GP2 zones from 1 h of aging. DSC and XRD results demonstrate the phase evolution of precipitates in alloys. The complementary observations by TEM show the size and morphology of the precipitates. The mechanical properties, such as the frequency-dependent storage modulus, hardness and tensile stress-strain curve, are also measured to characterize the strain glass transition or quantitatively correlate with significant precipitation hardening.