Whether it is diamond beads, saw segments or small saw blades, the service life of pressureless sintered diamond tools is basically unable to match that of pressure sintered ones. What are the underlying reasons?
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The key factors are summarized as follows:
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1. Insufficient matrix "holding force" on diamond grains — this is the core cause of the lifespan gap.
Hot pressing sintering:
During the pressurization process, matrix powder turns plastic at high temperatures. It is forced to compress and tightly encase the diamond grains, forming a strong mechanical interlocking effect. This robust "gripping force" effectively prevents premature dislodgment of diamond grains under load.
Pressureless sintering:
Densification relies primarily on capillary force generated by the liquid phase. This process is relatively "gentle", which may lead to inadequate wetting and wrapping of the hard, smooth diamond surfaces. If the interfacial bonding between diamond and matrix (encompassing both physical encapsulation and chemical bonding) is weak, diamond grains tend to fall off entirely before they can fully exert their cutting performance, resulting in a sharp decline in tool service life.
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2. Lower intrinsic strength and toughness of the matrix material
Hot pressing sintering:
External pressure effectively promotes atomic diffusion between powder particles, breaks down oxide films on particle surfaces, and refines the grain structure. As a result, the matrix material produced via hot pressing generally exhibits higher strength, hardness and toughness.
Pressureless sintering:
Without the assistance of sufficient external pressure, densification and intergranular bonding strength achieved solely through solid-state and liquid-phase sintering often fail to reach the levels of hot pressing. This is especially true for high-melting-point, high-strength skeleton materials (e.g., tungsten-Cobalt Alloys). Pressureless sintering struggles to form strong metallurgical bonds between these materials, leaving the matrix relatively "soft" or "brittle". The resulting poor wear resistance means the matrix cannot provide stable support for the diamond grains.
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3. Process stability and porosity issues
Hot pressing sintering:
External pressure effectively inhibits the growth and coalescence of pores, and rapidly closes existing voids. This ensures high process stability and excellent product consistency.
Pressureless sintering:
The process is extremely sensitive to sintering temperature, duration and atmospheric conditions. Even minor deviations in process control can lead to uneven shrinkage, deformation or residual porosity, particularly in large-sized products (such as long diamond beads). These pores act as crack initiation sites, which propagate rapidly during tool operation and ultimately cause premature fracture or failure.
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Technicians at Sagwell hold the view that the potential of current pressureless sintering technology lies in compensating for these inherent drawbacks through advanced material solutions (e.g., high-performance
Pre-Alloyed Powders, addition of active elements to enhance interfacial bonding) and precise process control (such as post-sintering heat treatment). This approach can help narrow the service life gap between pressureless and hot pressing sintered diamond tools.
