A GEORGIA-BASED COMPANY has begun commercial production of improved high-performance titanium diboride materials using a patented high-energy chemical reaction process first developed to make armor for U.S. Army tanks. Initial applications for the high-temperature, wear-resistant materials include cutting tools, dies and electrodes.
Dr. Kathryn Logan holds sample parts made of titanium diboride. That material and titanium diboride-alumina are proving superior, in several ways, to traditional materials.
Advanced Engineered Materials, LLC, has licensed a self-propagating high-temperature synthesis (SHS) process for manufacturing high-purity titanium diboride (TiB2) and titanium diboride-alumina composite (TiB2-Al203). The company is developing other uses for the material, the composite, and the SHS processing technique, which uses an energetic oxidation-reduction reaction to generate temperatures of up to 3,000 degrees Centigrade. Also known as combustion synthesis, the thermite reaction process resembles the chemical reaction that creates fireworks displays.
The SHS process was developed by researchers at the Georgia Institute of Technology and assigned to the Georgia Tech Research Corporation, which has licensed it to Advanced Engineered Materials.
Titanium diboride and titanium diboride-alumina offer attractive properties, including electrical conductivity; wear resistance; high compressive and mechanical strength; resistance to chemical reactions, molten metals and thermal shock; high thermal conductivity, and the ability to withstand high temperatures.
"These materials are superior, in a variety of properties, to metals and other advanced materials. For instance, the hardness is superior to tungsten carbide, the thermal conductivity is better than cubic boron nitride, fracture toughness is greater than that of silicon nitride, and the stiffness-to-weight ratio is excellent," says John R. Winters, president and chief executive officer of Advanced Engineered Materials. "This balance works well in applications where molten metals or metal extrusions are involved. We are positioned to compete in these and other materials application markets."
Manufacturing has started, and Winters says the company hopes to have 18 employees working at its factory in Woodstock, Ga., by the end of 1996. The facility can produce 1.6 million pounds of advanced materials annually.
"Compared to conventionally produced titanium diboride, the chemically based SHS technique yields TiB2 material with smaller (submicron) particles, and allows the composite to be produced in final form within molds," says Dr. Kathryn V. Logan, associate director of Georgia Tech's School of Materials Science and Engineering and a consultant to the company. "Those differences mean lower costs for manufacturing."
Conventional titanium diboride synthesis relies on a solid state diffusion process that heats boron carbide (B4C) and titanium dioxide (TiO2) to a temperature of 2,000 degrees Centigrade. Some carbide material remains as a contaminant in the powder after synthesis, and the process produces large particles that must be ground into finer powder in cobalt-bonded tungsten carbide mills.
"The tungsten carbide and cobalt add more contaminants at grain boundaries of the titanium diboride particles," Logan says. "Because of the contamination, parts made from this carbothermic titanium diboride must be hot-pressed at high pressures and temperatures for extended periods to produce the density required for many applications."
By comparison, the SHS system uses powdered metal -- either magnesium (Mg) or aluminum (Al) -- titanium oxide (TiO2) and boron oxide (B2O3). The materials are mixed and placed into a high temperature crucible. The mixture is then ignited and the reaction between the two oxides and the metal powder proceeds to completion. Once started, the self-sustaining reaction reaches temperatures of more than 2,000 degrees Centigrade.
The reaction produces titanium diboride dispersed within either magnesium oxide or alumina, depending on the metal powder used. The magnesium oxide can be leached from that mixture, leaving only pure titanium diboride in particles that average a half-micron in size. (A human hair is 50 microns in diameter.) The small particles do not have to be ground, and because they are not contaminated by carbide materials, can be hot-pressed into finished products at lower temperatures (1,500 degrees Centigrade) in less time (2 to 4 hours) than the conventional materials, thus reducing manufacturing costs.
"The titanium diboride-alumina composite does not require further processing and offers many of the same properties of the pure material, though it costs less to produce and its melting point is lower," Logan says. "Processing conditions can be varied to produce either a dense composite material or a porous foam into which materials such as molten metals can be infiltrated."
Officials of Advanced Engineered Materials believe the high wear resistance of their titanium diboride will benefit companies that now use dies and cutting tools made from materials such as hardened steel, tungsten carbide or diamond.
"These companies have tremendous costs in replacement parts," Logan explains. "We can provide them with a material that will allow them to buy significantly fewer parts per year, compared to hundreds or thousands with the materials they are using now."
Beyond titanium diboride, the company hopes to explore other materials that can be produced with the SHS process, for which Logan has obtained nine patents.
"There are many technical criteria for high performance materials that the titanium diboride and titanium diboride-alumina composite fulfill, but they are just the starting points for other materials, other composites and other forming and synthesis techniques," she says. "Using the SHS technique with other processes would open many other possibilities."
Winters believes the worldwide exclusive licensing agreement for rights to the technology is good for all involved.
"Georgia Tech has done a good job of developing the technology," he concluded. "We are taking the next step, which is commercializing it."
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