Diamond-coated asphalt tool development

Tom passes around two physical samples — one with a silicon carbide tip brazed to a steel shank, one with a sintered diamond tip. Used to introduce the productivity-vs-replacement-market argument and to set up the Ashby plot. Production cost of sintered diamond couldn't be justified because silicon carbide gives adequate one-shift performance.

Someone asked me something yesterday at the end of class about diamond, and I was talking about structural materials last time. This is a product. The product goes together like this and there's another half I have in my office. Anybody know what this tool is?

[Tom holds up a composite cutting tool.] This is actually a composite material — a big heavy chunk of steel, with tungsten carbide brazed on the end, and the very tip is sintered diamond. It looks black because it's a bunch of diamond powders sintered together. It's a double-step braze. This is to reclaim asphalt on the highway. In the middle of the night they're taking the asphalt off and resurfacing. A machine comes along with a bunch of these — a big auger — and it breaks up the old asphalt and throws it in the truck, and the truck takes it back to the asphalt plant to be re-melted and recycled. The problem is the tips get a lot of abrasive wear, and the tungsten carbide, which is one of the hardest materials we have, basically wears out. You'd like it to last for an eight-hour shift, but they don't always.