PSI - Issue 77

Valeria Lemkova et al. / Procedia Structural Integrity 77 (2026) 279–291 Valeria Lemkova and Florian Schaefer / Structural Integrity Procedia 00 (2026) 000–000

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the need of a higher local geometrically necessary dislocation density massive hardening. These constraints introduce higher strain gradients with decreasing particle spacing. The smaller the particle spacing, the stronger the hardening becomes. If the interface stability is low, the large stress concentration at the interface has an additional impact: a lack of gain in yield strength and ductility compared to MMCs with high interface stability. If the interface stability is high, particle fracture dominates failure Romanova et al. (2009). But, particle fracture is also triggered by higher stress concentrations through edged particles. Premature ceramic / metal decohesion due to a low interfacial strengh is directly reflected in a decreased strain hardening potential Mortensen and Llorca (2010). This can lead to crack initiation under operation condition. Interfacial debonding a ff ects the tensile behavior more significantly than the spatial distribution of the embedded particles Segurado and LLorca (2005). Although the strength of the metal / ceramic interface is crucial for the mechanical performance of MMCs Rajan et al. (1998), only few papers have so far dealt with the interface properties of composites Moghadam et al. (2014). Most are limited to atomistic or finite element (FE) simulations Berner et al. (1999); Romanova et al. (2009). Experi mentally, bulk interfacial properties of composites have been locally probed by nanoindentation techniques Coughlin et al. (2009b,a) or elaborated micromechanical testing of specimens milled by focused ion beam (FIB) Luksch et al. (2021). Thus, on the one hand stabilization of the high grain boundary density of a nc matrix and on the other hand to implement a good bonding between the ceramic particles and the metal matrix is vital to achieve the goal for a high strength and ductile MMC. This is also imperative to functionalize the ceramic dispersoids in a future step. In this study, the extent to which the mechanical contrast between metal and ceramic particles a ff ects the manufac turability and particle bonding to the matrix was investigated. In addition, the analysis focuses on the microstructural evolution during fabrication and heat treatment with regard to microstructural stability. The feasabilty to combine the advantages of a high strength and metallic matrix with incorporated ceramic dispersoids without thermal loading was thereby established. For this purpose, micromechanical testing was combined with heat treatments partly in situ in scanning electron microscopy (SEM) and with microstructure assessment by transmission Kikuchi di ff raction (TKD).

2. Materials and Methods

2.1. Materials section

Since the mechanical contrast between matrix and ceramic embedment particles is expected to a ff ect severely the extent of the excess stresses at the interface, an influence on the distribution process and on the evolution of the microstructure is expected, too. Thus, the Young’s moduli of even the ceramics and the metal powders were varied. The chosen material net is given in Tab. 1.:

Table 1. Processed metals and ceramics manifold and their elastic moduli and powder grain sizes. metal modulus ( GPa ) max. size ( µ m ) ceramic

modulus ( GPa ) (ref.)

mesh size

Fe (b.c.c.)

206 200

30 40 25

Si 3 N 4 Al 2 O 3

220-312 (Zerr et al. (2002)) 376 (Broz et al. (2006)) 118 (Broz et al. (2006))

325 400

Ni Al

72

SiO 2 sand

< 10 µ m

mix

250

Although the elastic moduli given in Tab. 1 depend on the measurement method and the intrinsic elastic anisotropy of the material, a systematic approach was implemented. On the one hand, the modulus of Si 3 N 4 is in the range of the modulus of Ni and Fe, whereas the modulus of SiO 2 is similar to the modulus of Al. On the other hand, a parameter net can be tested for the elastic mechanical contrast with a sti ff er and also less sti ff er ceramics compared to the matrix metal. The e ff ect of stress state in the combination of SiO 2 in Ni or Fe is of special interest, because a compression state is expected near the interface, whereas for the other combinations a tension stress state is expected as discussed in the literature and already-mentioned above. A compression stress state is expected to stabilize the particle and the interface bonding with less influence on the evolution of the grain size distribution in the vicintiy of the interface.