Issue 78

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

counterbody sinks on the surface of the material causing a more severe wear loss. The debris particles thus formed adhere to the surface causing material transfer (Fig. 16 (a)). The loose fragments of debris due to repeated sliding, may break and contribute to the third -body wear which explains the abrasive wear marks seen in the bare 16Cr5Ni MSS. The boronized surface is much harder than the bare surface and hence the counterbody does not sink much into the sliding surface. However, due to the combined action of corrosion and wear in the tribocorrosion condition, spalling and delamination of the boronized layer creates hard debris particles leading to fracture at specific areas. These debris particles act as abrasives contributing to three body wear mechanisms and the uneven surface creates uneven contact between the sliding surfaces and therefore abrasion and considerable plastic deformation can be seen on the worn surface of the counterbody. However, the tribo-oxidation mechanism observed in the case of 16Cr5Ni MSS boronized at 950°C may be the reason for the severe wear damage seen on the surface of the counterbody. Further, as per ASTM G119 standards, the specific contributions of corrosion and wear are calculated. Also, synergy (S) during tribocorrosion is also calculated as shown in Tab. 5. The negative values of S indicate antagonistic relation between wear and corrosion.

W (Dry wear rate, mm 3 /Nm)

T (Tribocorrosion wear rate, mm 3 /Nm)

C (Corrosion contribution) mm 3 /Nm

S(Synergy) S=T-W-C mm 3 /Nm

Elements

0.157 0.247 1.748 2.129 1.121 2.040

-11.26

13Cr4Ni MSS

Bare

36 28

24.9

-8.15 -2.75 -2.67 -2.22 -2.94

Boronized at 950°C

20.10

Boronized at 1000°C

3.8

2.80

16Cr5Ni MSS

Bare

5.1 3.5

4.60 2.40

Boronized at 950°C

Boronized at 1000°C

4.8

3.90

Table 5 : Tribocorrosion quantitative parameters.

C ONCLUSIONS

T

he effect of boronizing on the tribocorrosion performance of 13Cr4Ni and 16Cr5Ni MSS is evaluated. Potentiodynamic polarization tests with sliding, dry sliding wear and simultaneous potentiodynamic polarization and sliding wear tests in the presence of 3.5 wt. % NaCl solution were carried out on the bare and boronized samples. The key findings of this study are:  The tribo-corrosion behavior of 13Cr4Ni and 16Cr5Ni martensitic stainless steels is greatly affected by boronizing, which increases surface hardness ( ≈ 1680-1805 Hv) but decreases corrosion resistance. Due to chromium depletion and inadequate passivation, the boronized samples exhibit a shift in corrosion potential of about 200-310 mV and an increase in corrosion current density from approximately 0.6–0.9 µA/cm² (bare) to approximately 4–8 µA/cm², reaching approximately 14–27 µA/cm² during tribo-corrosion.  Boronizing temperature has a significant impact on wear performance in dry sliding circumstances. At 950 °C, the coefficient of friction is lower, ranging from 0.49 to 0.78. Wear rates range from 3.5 × 10 -6 to 5.1 × 10 -6 mm³/Nm, with a 25-27% decrease at 950 °C. Increased brittleness and decreased fracture toughness (~2.6-2.8 MPa √ m) as opposed to ~3.3-3.9 MPa √ m are associated with higher wear at 1000 °C.  The coefficient of friction in tribo-corrosion is reduced to 0.28-0.49 when 3.5 weight percent NaCl is present, which is a drop of roughly 16-33% when compared to dry sliding. Boronized samples have far better wear resistance, with wear rates lowered by 60-80% when compared to bare steels but have inferior corrosion resistance. The electrolyte's lubricating effect and the development of protective tribofilms are responsible for this.  Cyclic passivation and depassivation control the wear mechanisms under tribo-corrosion, which include abrasion, adhesion, and tribo-oxidation. The ideal ratio of toughness to hardness is achieved by boronizing at 950°C. Despite decreased corrosion resistance, boronizing generally improves tribo-corrosion performance, making it appropriate for applications where wear and corrosion occur simultaneously.

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