Recently, a team led by Professor Di Zhang, an Academician of the Chinese Academy of Sciences, and Professor Qiang Guo at Shanghai Jiao Tong University (SJTU) has shown how ceramic particles can help metals deform more uniformly. The mechanism relies on the metal gradually releasing its constraint on the particles, allowing them to change crystal structure and expand as the composite is stretched.
The research was conducted at SJTU’s State Key Laboratory of Metal Matrix Composites and School of Materials Science and Engineering, in collaboration with Nanyang Technological University (NTU), Singapore; Dongguan University of Technology; the Institute of High Energy Physics, Chinese Academy of Sciences; and the Spallation Neutron Source Science Center. The paper, “Transformation-induced plasticity in metals activated by shape-memory ceramics,” has been accepted for publication in Physical Review Letters.
Aerospace and transportation applications call for lightweight materials that can carry high loads and tolerate damage. Adding ceramic particles to a metal can increase its stiffness and strength, but the hard, brittle particles tend to concentrate stress and strain, reducing ductility and toughness. Shape-memory ceramics can accommodate some deformation by changing their crystal structure. The difficulty is that the stress needed to trigger this change is usually higher than a soft metal matrix can supply.
Building on earlier studies (Nature Communications 14, 7103, 2023; Acta Materialia 276, 120118, 2024; Materials Research Letters 13, 51-59, 2025), the team used cerium-doped zirconia particles in aluminum as a model system. During processing, constraint from the surrounding aluminum stabilizes the zirconia particles in a metastable tetragonal structure. As the metal stretches, local constraint gradually relaxes, allowing the zirconia to transform to its monoclinic structure and expand (Figure 1). Constraint relief therefore enables transformation even when the matrix is too soft to trigger it directly.
Figure 1. How matrix constraint controls ceramic phase transformation. Processing retains metastable tetragonal zirconia within aluminum. During stretching, local constraint relaxes, allowing transformation to the monoclinic phase and lattice expansion. The schematic illustrates atomic arrangements and the associated free-energy changes.
The composite containing 20% zirconia by weight achieved a uniform elongation of 7.3%, compared with 3.7% for a control containing the same amount of non-transformable zirconia. Uniform elongation measures how far a sample stretches before deformation concentrates into a narrow neck. The transformable composite also reached an ultimate tensile strength of 296 MPa, about 50% above the 197 MPa of pure aluminum, while retaining a total elongation of about 13% (Figure 2).
Figure 2. Tensile properties of aluminum composites containing transformable zirconia. (a) Transformable and non-transformable particle controls. (b) Effects of particle content. (c) Strain hardening and dislocation-density evolution. (d) Comparison of measured properties with rule-of-mixtures predictions. TE-Al and NE-Al denote transformation-engineered and non-engineered aluminum composites containing transformable and non-transformable zirconia, respectively. Both are prepared by the same process.
The team combined neutron diffraction on pre-strained, unloaded samples with in situ micro-tensile tests, Raman spectroscopy, and electron microscopy to trace the transformation across length scales. As the particles expand, they promote dislocation storage in the surrounding aluminum, helping it continue to harden during deformation. This sustained strain hardening delays necking. The transformation also improves deformation compatibility between the particles and matrix and limits early crack development (Figure 3).
Figure 3. Evidence linking ceramic transformation to deformation across length scales. Neutron diffraction, digital image correlation, in situ micro-tensile testing, and electron microscopy connect phase evolution with strain distribution, particle expansion, and dislocation evolution. Neutron diffraction measurements were performed on pre-strained samples after unloading.
The team also demonstrated the mechanism in an aluminum-copper alloy and in aluminum containing metastable nickel-titanium particles. The results show how the stability of embedded phases, and the constraint imposed by the matrix, can be used to control deformation. This offers a route to structural metals whose reinforcements respond to loading and help the material accommodate damage.
The paper’s first author, Dr. Wangshu Zheng, earned his Ph.D. through the SJTU–NTU joint program and is now a research associate at the University of Oxford. The corresponding authors are Di Zhang, Qiang Guo, and Lei Zhao of SJTU; Chee Lip Gan of NTU; and Runxia Li of Dongguan University of Technology. SJTU is the lead institution.
The work was supported by the National Natural Science Foundation of China (Grant Nos. 52192595, 523B2005, and 52571174). Zheng also acknowledges support from the SJTU Outstanding Ph.D. Graduate Development Scholarship. The research used facilities at NTU’s Facility for Analysis, Characterisation, Testing and Simulation (FACTS).
The authors thank Xuejun Jin (SJTU), and Zehui Du and Moses James Paul (NTU), for discussions. They also acknowledge technical support from Shaopeng Li, Ge Wang, Yuyang Liu, Zhongxin Zhao, and Shuangyue Jia (SJTU); Ruqing Cao and Dalong Wen (Institute of Metal Research, Chinese Academy of Sciences); and Yinjie Ruan (Shanghai Institute of Ceramics, Chinese Academy of Sciences).
Article link: https://doi.org/10.1103/6bb2-hy7q