Michael D. Wheeler
Three years after unveiling an advanced method for depositing diamond thin coats, QQC Inc. has disclosed that it used the same three overlapping pulsed lasers to improve the surface of metals, ceramics and polymers.
The multilaser process gained attention (Photonics Spectra, June 1996, page 34) by creating diamond films several thousand times faster and more efficiently than chemical vapor deposition. The technique employs three lasers: one excimer (a KrF at 248 nm or an XeCl at 308 nm); an Nd:YAG at 1064 nm; and a CO2 at 10.6 µm.
As news of the discovery spread, the company received a flood of inquiries about such diamond coating applications as helicopter blades, artificial hip joints, scalpels and engine parts. Surgical tools with the QQC treatment will soon be on the market.
Rustum Roy, a professor of materials research at Pennsylvania State University in University Park, says QQC has expanded far beyond diamond coatings. At a December 1997 meeting of the Materials Research Society, he said the method dramatically transformed many commercial metal parts including a fuel-injector nozzle made out of an iron-silicon alloy, cladding it with a titanium carbide shell.
The shock of the high-power excimer laser combined with the temperature of the CO2 laser caused a cloud of white plasma. Engineers dropped fine titanium carbide powder mixed with a carbon-rich gas into the white plasma cloud. Seconds after the plasma absorbed the titanium carbide, the iron-silicon nozzle emerged clad in a titanium carbide surface -- several times harder than the original surface. All this occurred without melting or causing visible changes to the nozzle.
Pravin Mistry, co-founder of QQC and developer of the method, said he already has used the technique to harden the surfaces of both steel punches and golf clubs. In the case of steel punches -- used to form aluminum soft drink cans -- the cladding extended the lifetime of the punch tenfold.
In the diamond-producing process, the three lasers heated an area on a surface in the presence of CO2 and a nitrogen shielding gas stream. The resulting plasma produced a diamond crystal lattice with a metallurgical bond to the surface. The technique made diamond thin films at a rate of 3.6 mm per hour.