Effect of Si₃N₄ addition on the morphological and structural properties of the 316L stainless steel for nuclear applications

Abstract

The effect of the submicrometer-sized Si 3 N 4 addition on the morphological and structural properties of the ceramic dispersion strengthened (CDS) 316L stainless steels prepared by powder technology has been studied. Two composites were prepared: 316L/0.33 wt. % Si 3 N 4 and 316L/1 wt. % Si 3 N 4 . In order to assure a good dispersion of the ceramic particles in the stainless steel powders and a grain size reduction at the same time, the high efficient attrition milling has been used. Spark plasma sintering (SPS) was used for fast compacting of milled composites. Structural and morphological changes were studied after milling and sintering process. It was found that the amount of Si 3 N 4 addition influenced the efficiency of milling process resulting in powder mixtures with different 316L stainless steel grain size and shapes. In the case of 0.33 wt. % Si 3 N 4 addition, the flat 316L stainless steel grains with submicrometer size in thickness have been resulted after milling compared to 1 wt. % Si 3 N 4 added powder mixtures which consisted of almost globular 316L stainless steel grains with 50-100 μm in diameter. The intensive milling assured an optimal coverage of 316L stainless grains with Si 3 N 4 submicrometer-sized particles in both cases as demonstrated by energy dispersive spectroscopy (EDS) and TEM. On the other hand, the 316L phase has been maintained during and after the milling and sintering. The partial phase transformation of α-Si 3 N 4 to SiO x was observed by EDS.

Novel Alumina Dispersion-Strengthened 316L Steel Produced by Attrition Milling and Spark Plasma Sintering

“…A comparison of the XRD diffraction patterns of the starting powders and the milled powders (Figure 6) confirmed that the powders had a crystalline structure of an FCC γ-Fe The formation of a small fraction of the α phase was related to a partial phase transformation induced by the severe plastic deformation during the milling process. The formation of a similar α phase after milling was observed in our previous work on Si 3 N 4 [16] and SiC [15] dispersion-strengthened 316L steel. Al-Joubori et al observed the formation of a similar α phase [38].…”

“…This increase in the microhardness values was related to the addition of the harder nanosized alumina particles and to the presence of hardened particles as a result of the severe plastic deformation during the attrition milling process. Both the 316L/Al 2 O 3 composites showed lower microhardness results compared with the other composites prepared by the same process [15,16,42,43] (Figure 9).…”

“…This increase in the microhardness values was related to the addition of the harder nanosized alumina particles and to the presence of hardened particles as a result of the severe plastic deformation during the attrition milling process. Both the 316L/Al2O3 composites showed lower microhardness results compared with the other composites prepared by the same process [15,16,42,43] (Figure 9). It was proven by Chattopadhyay et al in their study on the microstructure/phase evolution in mechanical alloying/milling of stainless steel and aluminium powder blends that no considerable changes in the lattice parameters of the face-centred cube structure were observed in 316L alloys with an aluminium percentage lower than 25 wt% [41].…”

“…The Si 3 N 4 particles' distribution along the grain boundaries of the sintered samples were observed by TEM. The different grain morphologies and the agglomeration of Si 3 N 4 in the case of 316L/1 wt% Si 3 N 4 directly affected the microhardness and the flexural strength of the sintered composite, where lower values were measured in comparison with the 316L/0.33 wt% Si 3 N 4 [16]. Recently, many researchers have intensively developed and investigated aluminium-containing alloys/composites as promising construction candidates for future nuclear reactors [17,18].…”

The Effect of the Chemical Composition to the End-Properties of Ceramic Dispersed Strengthened 316L/Y2O3 Composites

“…The 316L/Y 2 O 3 composites are harder than the 316L reference sample as it is represented in Fig 12. The HV values: 1.75±0.05, 2.63 ± 0.32 and 2.33 ± 0.165 GPa have been measured for the 316L (reference), 316L/0.33wt% Y 2 O 3 and the 316L/1 wt% Y 2 O 3 respectively. The 316L/ 0.33wt% Y 2 O 3 composite was showing somewhat higher hardness values than the 316L/1 wt% Si 3 N 4 composite from our previous work [20]. The friction coefficient dropped with addition of Y 2 O 3 .…”