Slide Member Overlay Crystal Orientation Fatigue Resistance
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Solution Overview
Problem
Slide members in internal combustion engines face challenges in improving fatigue resistance without degrading embeddability and conformability, particularly with overlays made of Bi or Bi alloys which are brittle and lack the fatigue resistance of Pb alloys.
Innovation Solution
The solution involves forming the overlay with regions having different orientation indices in the thickness direction, utilizing a structure where the orientation index of crystal planes differs between the sliding-surface side and the base-material side, achieved through controlled Miller indices and ultrasonic wave frequencies during plating, allowing for improved fatigue resistance without thinning the overlay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the overlay is thinned to improve fatigue resistance, then fatigue resistance is improved, but embeddability and conformability are degraded
Solution Approach 1:
The overlay is designed with non-uniform crystal grain structure where the inner layer has columnar crystal grains oriented perpendicular to the sliding surface for fatigue resistance, while the outer layer has equiaxed or fine crystal grains for embeddability and conformability. This local differentiation of microstructure allows each region to optimize its properties for specific functional requirements.
Solution Approach 2:
The overlay is segmented into multiple layers with distinct thicknesses and microstructures. The inner layer near the base material has larger columnar grains, while the outer layer has smaller equiaxed grains. This segmentation allows the thicker inner layer to provide fatigue resistance while the thinner outer layer maintains embeddability and conformability without requiring overall thinning of the overlay.
2Object-affected harmful factors
If Bi or Bi alloy is used as overlay material to replace Pb, then environmental burden is reduced, but fatigue resistance is degraded due to brittle nature of Bi
Solution Approach 1:
The crystal grain orientation parameter is changed from random or equiaxed structure to columnar structure perpendicular to the sliding surface. This parameter change in grain orientation transforms the mechanical properties of brittle Bi material, enabling it to achieve fatigue resistance comparable to Pb alloys while maintaining the environmental benefits of Bi substitution.
Solution Approach 2:
The overlay uses a composite microstructure combining columnar crystal grains in the inner layer with equiaxed or fine crystal grains in the outer layer. This composite microstructure leverages the strengths of different grain types to simultaneously achieve fatigue resistance from the columnar grains and improved ductility/embeddability from the equiaxed grains, overcoming the inherent brittleness of Bi material.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances fatigue resistance while maintaining embeddability and conformability, achieving results similar to a thinned overlay without the thickness reduction, and can be effectively applied using Bi, Bi alloys, or other materials like Ag and Ni alloys.
Implementation Method 1
the orientation index of a crystal plane differs in the thickness direction of the overlay. This is believed to be attributable to a thin film effect of the overlay.
Implementation Method 2
achieved through controlled Miller indices and ultrasonic wave frequencies during plating
Data Source
AI summary
A slide member is provided with a base material and an overlay provided over the base material. The overlay includes a plurality of regions in a thickness direction including a region located in sliding-surface side that slides with the counter element and a region located in a base-material side. A material forming the overlay includes a plurality of crystal planes. Orientation index of at least one of the crystal planes differs in the region located in the sliding-surface side and the region located in the base-material side of the overlay.