Mn+ 1AXn（MAX）相屬於三元碳化物和氮化物結構，其中M為前過渡金屬元素，A為13-16主族元素，X為C或N元素。和傳統陶瓷不同的是, 可加工的MAX 相具有獨特的物理化學性質，例如低密度，高強度，出色的抗熱衝擊和耐損傷效能。MAX相由於其高溫穩定性，使其適用於極端環境溫度中的結構應用，譬如核電和航空航天推進系統。透過調整MAX晶體結構的成分，可以進一步控制這些化合物的化學、機械、磁性和熱學性質。然而，在高溫和氧化條件下，大多數MAX相都會經歷不利的自我維持氧化反應，從而導致機械完整性的破壞。因此，評估MAX相的氧化行為對於將其進一步發展為高溫結構或塗層材料至關重要。由於氧化過程非常複雜且計算模型代價大，目前尚沒有一種能夠快速評估任意MAX相化合物的氧化物相穩定性的計算方法。
來自美國德州農工大學材料科學與工程系的P. Singh和R. Arroyave教授團隊發展了一種機器學習驅動的高通量方法，用於快速評估M2AX相的穩定性和氧反應性。這個提出的高通量方案能夠快速評估大合金空間的氧化穩定性，並減少設計時選擇合金的時間和成本，這種方法比使用DFT常規方法快了幾個數量級。
作者們用機器學習驅動高通量正規化，快速評估了211種MAX相M2AX的穩定性和氧反應性。所提出的方案透過結合基於機器學習模型的獨立篩選的稀疏演算法和巨正則線性程式設計，用以評估MAX相在氧化過程中與溫度相關的吉布斯自由能、反應產物以及元素的化學活性。透過充分評估Ti2AlC的組成元素對於氧氣的熱力學穩定性和化學活性，以瞭解其高溫氧化行為。該預測與在Ti2AlC上進行的氧化實驗非常吻合。不僅如此，還揭示了在實驗上無法合成Ti2SiC的亞穩態是由於競爭相具有更高的穩定性。對於所提方法的一般性，作者們對Cr2AlC的氧化機理作了分析討論。對氧化行為的瞭解將有助於更有效地設計和加速發現具有在高溫氧化環境中保持效能的MAX相。
該文近期發表於npj Computational Materials 7: 6 (2021)，英文標題與摘要如下，點選https://www.nature.com/articles/s41524-020-00464-7可以自由獲取論文PDF。
High-throughput reaction engineering to assess the oxidation stability of MAX phases
D. Sauceda, P. Singh, A. R. Falkowski, Y. Chen, T. Doung, G. Vazquez, M. Radovic & R. Arroyave
The resistance to oxidizing environments exhibited by some Mn+1AXn (MAX) phases stems from the formation of stable and protective oxide layers at high operating temperatures. The MAX phases are hexagonally arranged layered nitrides or carbides with general formula Mn+1AXn, n = 1, 2, 3, where M is early transition elements, A is A block elements, and X is C/N. Previous attempts to model and assess oxide phase stability in these systems has been limited in scope due to higher computational costs. To address the issue, we developed a machine-learning driven high-throughput framework for the fast assessment of phase stability and oxygen reactivity of 211 chemistry MAX phase M2AX. The proposed scheme combines a sure independence screening sparsifying operator-based machine-learning model in combination with grand-canonical linear programming to assess temperature-dependent Gibbs free energies, reaction products, and elemental chemical activity during the oxidation of MAX phases. The thermodynamic stability, and chemical activity of constituent elements of Ti2AlC with respect to oxygen were fully assessed to understand the high-temperature oxidation behavior. The predictions are in good agreement with oxidation experiments performed on Ti2AlC. We were also able to explain the metastability of Ti2SiC, which could not be synthesized experimentally due to higher stability of competing phases. For generality of the proposed approach, we discuss the oxidation mechanism of Cr2AlC. The insights of oxidation behavior will enable more efficient design and accelerated discovery of MAX phases with maintained performance in oxidizing environments at high temperatures.