Effects Of Additives On Properties Of Molybdenum-based Materials

As one of the metals with strategic significance, Molybdenum owns the high melting point, good corrosion resistance, electric and heat conduction. However, the popularization and application as structure materials is limited greatly because of its low wear resistance. Molybdenum recourse of our country reserves rank first in the world, while there is a great gap on molybdenum processing between china and other countries in the world. So it is very necessary to develop new molybdenum-based materials. Combing molybdenum with ceramic can get cermet materials, which own the advantages of metal and ceramic. At the same time, rare earth oxides can be served as stabilizer and grain growth inhibitor, which can change microstructure of materials. So developing molybdenum-based materials by adding rare earth oxides and ceramic has important realistic meanings. In this study, Microstrure, wear resistace and corrosion resistance of Molybdenum-based materials with additives were researched.In this paper, Mo-CeO2, Mo-Cr2O3, and Mo-Al2O3-CeO2 composites were made by pressless sintering. Sintering properties were tested. Sintering phases and microstructure were analyzed by XRD, EPMA and SEM. The analysis shows that both ceria and chromium oxide can promote sintering effect to Molybdenum materials, while the effect to Mo-Al2O3-CeO2 composite is little. Ceria, chromium oxide can inhibit the grain growth of molybdenum. CeAl11O18 can be found with the addition of Ceria. And with the increasing of Ceria, the amount of CeAl11O18 increases while Alumina becomes less. Alumina absolutely disappears when the volume fraction of ceria arrives at 6%, which is replaced by CeAl11O18. In theory, when the amount of substance of Ceria and Alumina ratio is 0.182, Alumina change into CeAl11O18. The formation mechanism is shown as follow: 2CeO2+11Al2O3→2CeAl11O18+1/2O2. The phases of Al2O3+CeAl11O18 and distribute as dots and strips. Circle blunt morphology appears at the phase boundary of Molybdenum. Wear resistance of Mo-Al2O3-CeO2 composites was tested by MM200 wear machine, and wear morphology was analyzed by SEM. The results show that the friction coefficient decreases firstly and then increase with the increasing of volume fraction of Ceria at the load of 50N and 70N, while it always increase at the load of 90N. Wear resistance was mainly influenced by relative density, only little by volume fraction of ceria. The wear mechanisms of Mo-Al2O3-CeO2 composite are abrasive wear, adhesive wear and mechanical grinding, which accord with spalling theory.Corrosion resistances in nitric acid, sulfuric acid and hydrochloric acid were investigated by complete immersion at room temperature. The research results show that the corrosion rate in nitric acid is greater than in the sulfuric acid and hydrochloric acid. Mo-Al2O3-CeO2 composites with 6vol.% ceria perform better corrosion resistance in the nitric acid and sulfuric acid than the composites with 2vol. %,4vol.%,8vol.%, while perform poor corrosion resistance in hydrochloric acid. The phase of molybdenum was corroded firstly in nitric acid by chemical corrosion and micro-electrochemical corrosion; the boundaries of molybdenum and Al2O3+CeAl11O18, CeAl11O18 were corroded firstly in sulfuric acid; pitting corrosion appeared in hydrochloric acid.