Metal Surface Carbon-Nitrogen Gradient Hardening for Scratch Resistance
Solution Overview
Problem
Conventional methods for enhancing the scratch resistance and adhesion of metal surfaces in electronic devices, such as smart phones and smart watches, result in either poor bonding or easy peeling of the hardening layer, leading to aesthetic issues.
Innovation Solution
A carbon-nitrogen gradient hardening layer is formed on the metal surface through a vacuum process using a mixed gas of acetylene, nitrogen, and hydrogen, followed by glow discharge, with controlled temperature and pressure conditions, and subsequent removal of part of the carbon layer to achieve a hardness gradient that improves adhesion and scratch resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hardening layer is formed on the metal surface to improve scratch resistance, then the surface hardness is improved, but the adhesion between the hardening layer and metal body deteriorates, causing easy peeling
Solution Approach 1:
The patent applies local quality by creating a gradient hardening layer where the carbon-nitrogen composition varies through the thickness. The surface layer has high carbon content for hardness, while deeper layers have increasing nitrogen content for ductility and adhesion. This gradient structure ensures that each region has the appropriate properties for its function: the surface provides scratch resistance while the underlying layers provide bonding to the metal substrate.
Solution Approach 2:
The patent utilizes parameter changes by controlling the glow discharge process parameters (power, time, gas composition ratios of acetylene and nitrogen) to create different carbon-nitrogen concentrations at different depths. By adjusting these process parameters during treatment, the composition gradient is formed, transitioning from carbon-rich at the surface to nitrogen-rich near the metal interface, thereby achieving both hardness and adhesion.
2Strength
If the hardening layer is made harder to improve scratch resistance, then the surface durability is improved, but the bonding strength with the metal body deteriorates
Solution Approach 1:
The gradient hardening layer creates local quality variations where the surface region contains high carbon content for maximum scratch resistance, while the transition zone and substrate interface contain increasing nitrogen content for optimal bonding. This spatial variation in composition allows the surface to be extremely hard while maintaining strong adhesion through the nitrogen-enriched intermediate layers.
Solution Approach 2:
The patent creates a composite structure with varying composition through the thickness. The outer layer is carbon-dominant providing hardness, while the inner layer transitions to nitrogen-dominant providing adhesion. This composite gradient structure combines the benefits of both carbon (hardness) and nitrogen (bonding) in a single integrated layer, avoiding the peeling issue of uniform hard coatings.
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
The method results in a carbon-nitrogen gradient hardening layer with improved adhesion and scratch resistance, maintaining the aesthetic appearance of electronic devices by ensuring the layer is reliably attached to the metal body.
Implementation Method 1
creating a vacuum in the vacuum chamber to a first vacuum degree
Implementation Method 2
performing glow discharge so that a carbon-nitrogen gradient hardening layer is formed on a surface layer of the metal
Implementation Method 3
adding a mixed gas of acetylene, nitrogen and hydrogen into the vacuum chamber; performing glow discharge so that a carbon-nitrogen gradient hardening layer is formed
Data Source
AI summary
The disclosure provides a metal surface layer treating method, a metal assembly and an electronic device. The metal surface layer treating method includes: putting metal into a vacuum chamber, and vacuumizing the vacuum chamber to a first vacuum degree; adding a mixed gas of acetylene, nitrogen and hydrogen into the vacuum chamber; and heating the vacuum chamber to a temperature above an ambient temperature. In response to the temperature in the vacuum chamber reaching a first temperature value above the ambient temperature and a gas pressure of the vacuum chamber reaching a first pressure value, performing glow discharge so that a carbon-nitrogen gradient hardening layer is formed on a surface layer of the metal. The method includes removing part of a carbon layer of the surface layer of the carbon-nitrogen gradient hardening layer.