Cemented Carbide Surface Layer for Bonding and Strength
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Solution Overview
Problem
Cemented carbide articles with low Co content at the surface exhibit reduced fracture toughness and strength, along with poor wettability by brazing solders, leading to inadequate bonding with steel and difficulties in grinding complex shapes, making existing methods economically unfeasible.
Innovation Solution
A cemented tungsten carbide article with a surface layer comprising 5-25 wt.% W and 0.1-5 wt.% C, balanced with Co, Ni, or Fe, and optionally V, Cr, Ta, Ti, Mo, Zr, Nb, or Hf, applied through a specific sintering and cooling process to create a continuous surface layer enhancing strength and wettability, and an intermediate layer with higher binder content for improved mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the surface layer contains very little Co, then the hardness is maintained, but the fracture toughness and strength are reduced
Solution Approach 1:
The patent applies local quality by creating a surface layer with 5-25 wt.% W and 0.1-5 wt.% C balanced with Co, Ni, or Fe, which is distinct from the core composition. This surface layer has different properties (higher strength and fracture toughness) compared to the core, resolving the contradiction by allowing the surface to have optimized Co content for mechanical properties while the core maintains its original composition for hardness.
2Reliability
If the surface layer contains very little Co, then the hardness is maintained, but the wettability by brazing solders is poor
Solution Approach 1:
The patent creates a surface layer with specific composition (5-25 wt.% W, 0.1-5 wt.% C, balanced with Co, Ni, or Fe) that differs from the core. This surface layer has improved wettability by brazing solders due to the optimized binder content and composition, while the core maintains low Co content for hardness. The surface layer acts as an intermediate zone that facilitates bonding.
3Strength
If grinding is used to remove the surface layer with little Co, then the mechanical properties are improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by forming the desired surface layer with optimized composition (5-25 wt.% W, 0.1-5 wt.% C, balanced with Co, Ni, or Fe) directly during the sintering process, before any subsequent processing. This eliminates the need for post-sintering grinding operations to remove the surface layer, as the layer is already in its final desired state with proper thickness (2-20 microns) and composition.
Solution Approach 2:
The patent changes the sintering parameters to produce a surface layer with specific composition and structure. By controlling the sintering process parameters (temperature, atmosphere, time), the surface layer forms with 5-25 wt.% W and 0.1-5 wt.% C balanced with Co, Ni, or Fe, achieving the desired mechanical properties without requiring subsequent mechanical removal processes.
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 solution significantly enhances transverse rupture strength, fracture toughness, and wettability, resulting in improved bonding with steel and maintaining productivity without the need for grinding complex shapes.
Implementation Method 1
a core of tungsten carbide grains and a binder selected from cobalt, nickel, iron and alloys containing one or more of these metals
Implementation Method 2
the surface layer having a thickness of 2 to 20 microns and comprising 5 to 25 weight percent of tungsten and 0.1 to 5 weight percent carbon
Data Source
AI summary
The present invention relates to a cemented carbide article comprising a core of metal carbide grains and a binder selected from cobalt, nickel, iron and alloys containing one or more of these metals and a surface layer defining an outer surface for the article, the surface layer comprising 5 to 25 weight percent of tungsten and 0.1 to 5 weight percent carbon, the balance of the surface layer comprising a metal or alloy selected from the binder metals and alloys and the surface layer being substantially free of carbide grains as determined by optical microscopy or SEM. A method for the production of a cemented carbide article is also provided.