Figure 2 SEM micrographs of worn seat insert surface of engine #6175 after 1474 hours of testing. The arrows and labels indicate the locations of EDX analysis. The same adhesion phenomenon occurs on the valve seat surfaces. Figure 4 show... Figure 2 SEM micrographs of worn seat insert surface of engine #6175 after 1474 hours of testing. The arrows and labels indicate the locations of EDX analysis.
The same adhesion phenomenon occurs on the valve seat surfaces. Figure 4 shows SEM micrographs of the worn exhaust valve seat surface of engine #6175 after 1474 hours of testing. The valve material is Stellite 6 faced 23-8N (solution treated and aged). The arrows in Figure 4b indicate the locations of EDX analysis. Note the pits and deposits on the worn seat surface. Figures 5a shows the EDX spectrum of spot A on Figure 4b showing adhered insert material. Note molybdenum and manganese in the spectrum. Figure 5b shows the EDX spectrum of spot B in Figure 4b showing both adhered insert material and oil deposits. Note molybdenum.， phosphorous， chlorine， calcium， and zinc in the spectrum. Other valves from different engines labeled as "adhesion" in Table 2 share this typical adhesive phenomenon.
The adhesive wear mode appears to predominate at valve seat interfaces with high asperity contact stresses or high combustion pressure. The surface roughness can contribute to adhesion significantly. Valves faced with Stellite alloy show less adhesive wear than unfaced valves， Table 2. The presence of high melting point phases， such as carbide or ceramic compounds in the contacting materials is believed to help prevent microwelding or adhesion related wear.
Shear strain， also known as radial flow， is defined as the first derivative of the displacement， i.e.， . Figure 6 [8]. Shear strain controlled wear can characterized as a surface plastic deformation process. The wear is the result of the shear strain on the seat surface exceeding the plasticity limit of the material. The material is then detached or delaminated from the seating surface as wear particles. The typical appearance of shear strain controlled wear are ridges and/or radial flow of material on valve seats and inserts. Shear strain controlled wear sometimes is associated with adhesion. 展开
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