PSI - Issue 75

Jérémie BOUQUEREL et al. / Procedia Structural Integrity 75 (2025) 442–449 Jérémie BOUQUEREL/ Structural Integrity Procedia (2025)

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For SEM advanced observations, SEM-EBSD were carried out on the various zone of the fillet along and perpendicular to the valve axis. Kernel Average Misorientation (KAM) criterion as well as the Line Segment Method were considered for plasticity markers (Bouquerel et al. (2021)). Complementary TEM observations were performed on thin foils prepared by double jet technique and additional ion milling step.

Figure 1: Harley-Davidson WLA/WLC 1942 original valves; as-new (HDEN1) and used conditions (HDEU1)

3. Results and discussion 3.1. Material identification

Coupled EPMA and NDIA investigations have been carried out to ensure the nature of the investigated material (cf. Table 1). Harley-Davidson WLA/WLC exhaust valves composition is very close to the Silchrome composition of the Japanese 1940s standard (Yamanaka (1942)).

Table 1. Harley-Davidson WLA/WLC exhaust valves EPMA-WDS analysis with reference valves composition or steel standards

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3.2. Hardness profile of the valve The hardness profiles of both HDEN1 and HDEU1 valves are reported in Figure 2. While hardness values remain similar in the stem areas (385 ц 16 vs 382 ц 18 HV1), at the valve head, a pronounced hardness decrease (120 HV) is measured for the used condition. These observations can be correlated with literature, which estimates the distribution of stress and temperature along the valve when the engine is operating (Cerdoun et al. (2020)). Indeed, the location of the hot exhaust gases emphasises the location of highest degradation in the valve. Hence, the approximate place at the valve fillet corresponding to maximum protrusion at fully opened position is marked in red in Figure 2. The stem part, under service, is exposed to much lower temperatures compared to the valve head. The softening attested by the