A technological advance in the treatment of metallic surfaces is under development by a team of researchers from the Physics Institute of the State University of Campinas (Unicamp) in partnership with the company Eaton, from the town of Valinhos in the state of São Paulo. The focus of the research is to make the transmission components of motorized vehicles – commonly known as gear boxes – more resistant. The process, named plasma nitration in vacuum furnace, is experimenting with, for the first time in the world, this type of component and is going to allow that the surface of the parts becomes harder, less subject to corrosion and to the effect of wear, producing improved performance and durability.
The implanting of the process is being financed by FAPESP through the Technological Innovation Partnership Program (PITE). At a budget of almost R$ 2 million, the project has the participation in 56% of the Brazilian division of the Eaton Corporation, the world leader in the manufacture of gear boxes. Part of the resources has been used to build the Ionic Implantation and Surface Treatment Laboratory, inaugurated in August at Unicamp. All of the equipment – furnace with a vacuum chamber, temperature control panel, and high voltage source for the generation of the plasma and internal distribution of gases – was projected by the researchers themselves and built in this country. The laboratory is a research and development plant with a high level of sophistication and can count upon advanced techniques of analysis and description.
The new research idea of the Unicamp group, coordinated by the physicists Daniel Wisnivesky and Fernando Alvarez, is based on the use of plasma furnaces for the nitration of metals, an advancement in relation to the thermo-chemical process in use throughout the metallic engineering industry, in order to alter the properties of surface hardness, corrosion and thermal resistance of the material. The conventional methods most widely used in Brazil make use of salt baths or gaseous nitration.
To nitride a metal means incorporating nitrogen ions into its surface. Afterwards these ions are thermally diffused into the metal, penetrating to around 0.5 millimeters into the part, forming nitrides, substances that give a greater hardness to the surface. In the process using plasma – an ionized gas containing electrons, ions, and neutral atoms – the metal parts are placed within a vacuum furnace in order to receive the treatment, at a pressure of between 1 and 10 millibars, equivalent to one thousand or ten times less than normal atmospheric pressure.
“The nitride formation using plasma presents a series of advantages on the traditional technologies”, says Wisnivesky. “The main one is that it generates minimum deformation on the parts, thanks to the lower temperature required in the process, of around 500° Celsius, and by the fact that it is being carried out in a vacuum oven”, he explains. In the traditional processes, the part is submitted to temperatures higher that 900° C, which leads to deformation. This demands that, after surface treatment, the part passes through a retooling process, making the process more expensive, and making it even longer.
The new technology is also more economic, because it consumes less energy. It also generates environmental gains by using clean and non-contaminating methods. “We make use of low quantities of non-toxic gases (nitrogen and hydrogen), while the conventional processes make use of toxic gases”, says Alvarez. As well as this, while the gaseous nitride produces on the surface of the metal a layer composed of frail characteristics called the “white layer”, the nitration with plasma generates a thicker covering, non-porous and very hard.
Besides its application on parts and components within the automobile industry, such as valves, gears and pistons, the nitration with plasma technique could well be used in forging, steel making, and the mechanics and hydraulics industries for the treatment of tools and tooling of metals, plastic injection molds, prostheses and aluminum molds. Currently, it is being used in the treatment of carbon steels, ferrous metals, alloys, refractory bricks, and more recently on the surfaces of aluminum.
One of the advantages of nitride ionization is the control of the process, via computer, that allows surface treatment in a controlled and uniform manner, on all of the part. For this reason, it is also possible to reproduce the operation several times, on different components, with the same level of efficiency. “Depending on the material, at the end of the treatment, the part gains a resistance of up to four times greater”, says Alvarez.
For Eaton, the partnership with Unicamp is highly advantageous. “They have the know-how in the area of nitration via plasma and are well trained in describing the characteristics of the material after the process”, explains the materials engineer Antônio Carlos Zambon, the manager of the sector for thermal treatment at the Eaton factory. In his opinion, if the process was to prove to be efficient in the technical part and economically viable, the company would study the implantation of an industrial plant to carry out plasma nitration. Eaton supplies its gear boxes to all of the main carmakers in the country and last year grossed US$ 200 million in Brazil. In the world, the company’s income reached some US$ 7.3 billion.
Technique on the rise
Nitration with plasma is a relatively recent technology, employed on an industrial scale for little more than fifteen years. “In Brazil this technique is little known. There are only two or three industrial companies that are making use of it, and even then with imported equipment”, says the physicist Wisnivesky. “In the entire world, we estimate that there are around three thousand industrial installations that make use of the process. Germany, France, Japan, the United States and Canada are the countries that are most advanced in this area”, Alvarez says. At the end of the 90s, there were no more than one thousand five hundred companies, which gives an idea of the evolution in the use of the technology.
Another piece of data that shows the importance of surface treatment by plasma is the increase, over the last few years, in the amount of scientific research and development work on this question. Between 1995 and 1999, in international magazines some one hundred and sixty research articles were published with respect to plasma nitration. For example, only in France these studies correspond to 21% of the total research papers in the area of surface treatment. The team from Unicamp has already published two articles in international magazines on this question and have presented another two at international congresses. With the new laboratory, these numbers and collaboration with other industrial companies should increase.
Industrial Application of Nitration Methods using Plasma Furnaces and the Ionic Implantation for Steel Treatment Used in Automobile Transmission Systems (nº 00/04706-5); Modality Technological Innovation Partnership (PITE); Coordinator Daniel Wisnivesky – Unicamp; Investment R$ 1,133,000.00 and US$ 40,000.00 (Eaton) and R$ 488,300.00 and US$ 155,120.70 (FAPESP)