Scientists at the International Advanced Research Centre for Powdered Metallurgy and New Materials (ARCI), Hyderabad, have developed a new method for making alloys of high strength. Austenitic steel, a special alloy, is among the promising structural materials used in power plants and reactors owing to excellent creep, corrosion and oxidation resistance compared with ferritic or ferritic–martensitic steels. It can withstand high temperatures, large stress, chemically reactive environments and intense neutron radiation fields, but suffers from inferior tensile strength and stress corrosion resistance at higher temperatures. Besides, one of the major concerns over its use in advanced nuclear power reactors is severe swelling due to irradiation, which can be reduced by introducing stable nano-oxide particles into the austenite matrix. The high-energy ball milling method used to disperse oxide particles in metal matrix invariably leads to powder sticking to the milling media and thus decreasing the milled powder yield. Using carbon-containing process control agents (PCA) such as stearic acid results in carbon pickup, which will promote coarsening of oxide particles.
A two-stage ball milling without the addition of any carbon-based PCA was employed by the ARCI scientists. The first-stage milling is aimed at dispersing the oxide particles into the ferrite matrix, which is the starting powder microstructure, and the second-stage milling is to transform the oxide dispersion strengthened (ODS) ferritic steel into austenitic ODS (AODS) steel by the addition of nickel.
Nitrogen gas was used as the PCA in both stages of milling to improve the milled powder yield. The alloy developed in this method was found to have one of the best combinations of yield strength and fracture strain.
Copper for silver
The shining grid lines you see in a photovoltaic solar module is silver, a costly metal, which is only expected to become dearer because the e-mobility and 5G telecom sectors will also want it. Can you use a cheaper metal in place of silver in PV cells?
Yes, says Dr Markus Glatthaar of the Fraunhofer Institute, Germany. Glatthaar, an expert in metallisation and structuring, has developed an electroplating process for the promising heterojunction technology to replace silver with copper. Copper is many times cheaper and more readily available than silver.
“We developed a special electroplating process that makes it possible to use copper instead of silver for the busbars,” explains Glatthaar. This even improves conductivity — the copper contact lines are particularly narrow on account of their laser structuring. The light-absorbing silicon layer experiences less shading than with silver lines. This improves electricity yield.
The Fraunhofer team also used aluminium as a masking layer. “We were able to adapt the process parameters and develop a special type of electrolyte which ensures that the aluminium’s extremely thin, native oxide layer can reliably fulfil its insulating function. This was an important milestone for the success of our research project,” says a press release from Fraunhofer Institute quoting Glatthaar.