Researchers from Lehigh University discovered that gallium nitride (GaN) material is surprisingly durable. In fact, they found that GaN has a sliding wear resistance that is second only to the most durable material known, diamond.
They also found that the sliding wear rate varied with crystal orientation and that wear rate varied by two orders of magnitude with increased humidity.
While previous studies looked at scratch resistance, the researchers noted that the sliding wear rate of GaN was not previously examined and compared.
The scientists conducted the wear experiments using a custom nano/ micro tribometer. They reciprocated a single crystal ruby ball (with a radius of 0.75 mm, Edmund Optics, Grade 25) against both GaN and InGaN materials on sapphire substrates with a sliding velocity of 1 m/s. The applied normal load for the reciprocation was 600 mN for GaN and InGaN (maximum Hertzian contact pressure 2 GPa, approximately 1/6 to 1/10 of the hardness of GaN) and 300 mN for InN with a maximum Hertzian contact pressure 1 GPa.
While most such experiments require only 1000 reciprocating cycles, the sliding wear rate of the GaN was so low that the scientists were not able to see wear after 1000 cycles. Instead, they performed 30,000 reciprocating cycles to show significant wear. They did the test both in the 1210 or 1100 crystallographic direction to separate the variability caused by the directionality.
The Lehigh University researchers reported their findings in an article in Applied Physics Letters.
The complex nature of the variation in slide wear resistance makes unclear any speculation about potential applications of GaN material for this kind of durability.