336 Prakt. Met. Sonderband 52 (2018) 
reaction phase formation is often described as a sheer diffusion process from carbide Ef 
forming elements into TiC particles. However, the sharp interfaces between (Ti,M)C and TiC ; 
as well as the non-continuous coverage of the TiC particles by (Ti,M)C suggest a nucleation 
and growth process of the reaction phase, rather than sheer diffusion. 
] Table 2: Results of the STEM/EDS analysis of TiC and the reaction phase 
Ti other | 
TiClat%] [54.2 1458 |- ~~ |- [- - FF 
36.0 (388 [122 [6.2 26 [1.1 0.2 
3.2 Formation Kinetics of the Reaction Phase 
Fig. 2 depicts the microstructure of the samples produced by three different HIP times. The 
images are composed of SEM/BSE micrographs on the upper right and the according 
quantitative phase analysis results, with TiC in blue and (Ti,M)C in red, on the lower left side. 
Fig. 2a shows the sample, which was consolidated for the shortest time (3.5 h). The reaction 
phase is visible as small bright spots at the TiC surface, which do not completely 
circumference the TiC particles. Fig. 2b represents the specimen which was consolidated 
for 6 h. Compared to the 3.5 h sample, the reaction phase has grown in thickness and 
completely surrounds some of the smaller TiC particles. The 24 h HIP time sample, depicted 
in Fig. 2c, shows the highest coverage of TiC particles by (Ti,M)C. Evaluating the phase 
formation by quantitative image analysis it was found that farem increases from 10, 11 to ong 
21 % for 3.5, 6.0 and 24 h HIP time. respectively. Lome 
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Fig. 2: Overlay of SEM/BSE micrographs and quantitative phase analysis (TiC in blue, 
(Ti,M)C in red) of M7 + 10 vol.% TiC for samples HIPed for (a) 3.5 h, (b) 6.0 h, (c) 24 h. 
To support the microstructural findings of the SEM/BSE investigation and to analyze the 
crystalline structure of the reaction phase, XRD experiments were conducted on the 
composite samples as well as on the original TiC powder. Fig. 3a depicts an overview of the 
whole XRD scan range, including the (111) and (200) carbide peaks, as well as the (110) 
martensite peaks. It was found that the reaction phase’s peaks are situated close to the TiC 
peaks but at higher diffraction angles. The lattice of the reaction phase could, thus, be 
identified as fcc, with a smaller lattice parameter compared to the TiC phase. The smaller 
lattice parameter is in good agreement with the smaller lattice parameter of VC and similar