Issue 78

N. Mohan et alii, Frattura ed Integrità Strutturale, 78 (2026) 129-145; DOI: 10.3221/IGF-ESIS.78.08

Figure 3: Potentiodynamic polarization curves of bare and boronized samples.

Dry sliding wear tests The evolution of the coefficient of friction (COF) for the boronized samples under dry sliding wear conditions is shown in Fig. 4. The COF of 13Cr4Ni and 16Cr5Ni MSS boronized at 950 and 1000°C varied from 0.57 - 0.78, 0.53 - 0.63, 0.59 - 0.65 and 0.49 - 0.55 respectively. Initially, the COF value increases steeply (upto 8 m), varies moderately between (8 - 72 m) (running-in period) and stabilizes after 74 m (steady-state). The COF values of MSS grades boronized at 950°C are lower compared to 1000°C.

Figure 4: Evolution of co-efficient of friction during dry sliding wear.

The highest value of COF is seen for 13Cr4Ni MSS boronized at 1000°C which also shows greater variation of the COF throughout the duration of the test. In comparison with the boronized MSS at 1000°C, the hardness of boronized MSS at 950°C is lower, yet the higher fracture toughness values (Tab. 2.) contribute to the reduction in COF. Further, boronized MSS at 1000°C the surface hardness is higher which limits the penetration of the counter body on the sliding surface, but the lower fracture toughness values and the inherent residual stress due to the additional borides present promote crack annihilation and propagation which therefore enhance the COF values [16]. Surface topographies of worn surfaces The 3D surface topographies of the worn surfaces are as shown in fig. 5. The surface topographies of both MSS boronized at 1000°C demonstrate deformed surfaces and several asperity points contributing to enhanced surface roughness. However, the surface topographies of the MSS boronized at 950°C are more even with deep grooves and wider tracks. Fig. 6. shows the wear scar profiles of all the boronized MSS samples. The depth of the scars is in the range

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