Near-Zero Thermal Expansion and High Strength in Multi-Phase La0.6Ce0.4(Fe0.91Co0.09)11.9Si1.1/Ag Compounds Produced Through Spark Plasma Sintering

The significant negative thermal expansion (NTE) that occurs in La(Fe,Si)13-based alloys during magnetic transition make them promising to combine with positive thermal expansion (PTE) materials to obtain near-zero thermal expansion (NZTE) materials. However, La(Fe,Si)13-based alloys with NTE generally show intrinsic poor mechanical properties. Here, thermal expansion properties are optimized by adding Ag in La0.6Ce0.4(Fe0.91Co0.09)11.9Si1.1 to form a multi-phase structure exhibiting enhanced compressive strength. Through spark plasma sintering (SPS) and annealing, the samples consisted of α-Fe(Co,Si), NaZn13-type, and LaAg2 phases. When the annealing temperature reaches 1323 K, LaAg2 disappears and is replaced by La2O3. The LaAg2 phase and α-Fe(Co,Si) phase contribute as PTE materials to compensate for the NTE of the NaZn13-type phase. Near-zero thermal expansion was achieved in the temperature range of 240–294 K, with a coefficient of thermal expansion (CTE) of 3.5 ppm/K at a 9.581 at.% Ag content. Benefiting from the uniform phase distribution and coordinated deformation, the samples obtained high mechanical strengths, with fracture stresses of 1481.1 MPa for the 15 wt.% Ag sample. This work provides a promising route for high-strength and near-zero thermal expansion Ag/La(Fe,Si)13 composites.