Hiroshima University 3D Prints One of the Hardest Metals on Earth

Tungsten carbide-cobalt is one of the hardest materials used in industry. It shows up in cutting tools, drills, machining equipment, and construction tools that have to withstand extreme wear and pressure. The problem is that it is expensive to make and wasteful to shape using conventional methods.

A team at Hiroshima University has now demonstrated a 3D printing approach that produces the material with industrial-grade hardness while using less of the costly raw feedstock.

Softening Instead of Melting

The researchers used hot-wire laser irradiation, a process that combines a laser beam with a preheated filler wire. Heating the wire before it reaches the work surface allows material to be added more quickly and efficiently. The key difference from traditional methods is that the process softens the tungsten carbide and cobalt rather than fully melting them. Fully melting tungsten carbide can alter its internal structure and reduce the hardness that makes it valuable.

The team tested two fabrication arrangements. In the first, the laser was directed onto the top of a cemented carbide rod. In the second, the laser led the process and irradiated the area between the bottom of the rod and the base material. Neither method fully melted the metals. Both softened them just enough to form and deposit the cemented carbide.

Defect-Free Hardness Above 1400 HV

The experiments produced base material with a hardness above 1400 HV. That measurement refers to Vickers hardness, a test that evaluates how strongly a material resists being indented by a hard tip. A value above 1400 HV places the resulting carbide among the toughest materials commonly used in industry, below only superhard substances such as sapphire and diamond.

The results differed depending on the fabrication arrangement. The rod-leading method caused some tungsten carbide to decompose near the upper portion of the manufactured structure, creating defects. The laser-leading method avoided those problems but initially struggled to maintain the required hardness.

The researchers addressed this by adding a nickel alloy-based middle layer. They also carefully controlled the temperature so that it remained above the melting point for cobalt but below the temperature at which grain growth occurs. Grain growth changes the microscopic crystals inside a material and can reduce its hardness and mechanical performance.

Less Waste, Lower Cost

Because additive manufacturing builds an object by placing material only where it is required, the approach can reduce the waste that comes with conventional powder metallurgy. Tungsten and cobalt are expensive raw materials, and conventional production can use a large amount of material while delivering a relatively limited yield.

The study was published in the International Journal of Refractory Metals and Hard Materials. The research team included scientists from Hiroshima University's Graduate School of Advanced Science and Engineering and Mitsubishi Materials Hardmetal Corporation.

What Comes Next

The researchers want to reduce cracking, improve durability, and determine how to manufacture more complicated shapes. Future work will focus on producing practical cutting tools, testing the process with additional materials, and finding ways to make the finished components even more durable.

If the technique can be refined for large-scale manufacturing, it could allow producers to place costly carbide only where it is needed. That would make advanced tools less wasteful and more economical while preserving the extreme hardness required for industrial use.