TEM investigation of ductile iron alloyed with vanadium.

This article presents results of the processing and microstructure evolution of ductile cast iron, modified by an addition of vanadium. The ductile iron was austenitized closed to the solidus (1095 degrees C) for 100 h, cooled down to 640 degrees C and held on at this temperature for 16 h. The heat treatment led to the dissolution of primary vanadium-rich carbides and their subsequent re-precipitation in a more dispersed form. The result of mechanical tests indicated that addition of vanadium and an appropriate heat treatment makes age hardening of ductile iron feasible. The precipitation processes as well as the effect of Si content on the alloy microstructure were examined by scanning and transmission electron microscopy. It was shown that adjacent to uniformly spread out vanadium-rich carbides with an average size of 50 nm, a dispersoid composed of extremely small approximately 1 nm precipitates was also revealed.

Mechanical alloying and high pressure processing of a TiAl-V intermetallic alloy.

An alloy with a chemical composition of Ti-45Al-5V (at.%) was synthesized by mechanical alloying in a Szegvari-type attritor from elemental powders of high purity. Before compaction, the powders were characterized by X-ray diffraction and scanning as well as transmission electron microscopy. The compaction of powders was carried out by hot isostatic pressing and hot isostatic extrusion. The resulting material was subjected to microstructural and mechanical characterization. The microstructure investigated by transmission and scanning electron microscopy supplemented by X-ray diffraction revealed that the bulk material was composed of a mixture of TiAl- and Ti(3)Al-based phases, however, the typical lamellar microstructure for such alloys was not observed. The materials exhibited exceptionally high yield strength together with satisfactory ductility and fracture toughness. The high strength was unequivocally due to grain refinement and the presence of oxide dispersoid.

Microstructure and mechanical properties of Nb15Al10Ti alloy produced by mechanical alloying and high temperature processing.

In this work, an Nb15Al10Ti alloy produced by mechanical alloying was investigated. The milling of elemental powders of Nb, Al as well as TiAl intermetallic phase resulted in the formation of homogenous niobium solid solution, Nb(ss), and refinement of powder particles. Powder after milling was consolidated by conventional hot pressing at 1300 degrees C under pressure of 25 MPa as well as by hot isostatic pressing at 1200 degrees C under pressure of 1 GPa. Microstructure of consolidated material was examined by transmission electron microscopy, scanning electron microscopy and X-ray diffraction. Materials after consolidation were composed of three phases: niobium solid solution Nb(ss), Nb(3)Al intermetallic phase and titanium oxide dispersoid TiO. The analysis of the mechanical properties indicated that both refinement of microstructure as well as introduction of ductile Nb(ss) into the microstructure contributed to very high yield strength and fracture toughness satisfactory for this strength.

Influence of plastic deformation and prolonged ageing time on microstructure of a Haynes 242 alloy.

The material used in this study was a commercial HAYNES alloy 242 with a nominal composition of Ni-25% Mo-8% Cr (in wt.%). In the standard heat treatment, the 242 alloy is annealed at a temperature between 1065 and 1095 degrees C and then water quenched. The ageing treatment is carried out at 650 degrees C for 24 h in order to develop the long-range-order strengthening. The alloy in the conventionally aged condition was additionally cold rolled to 50% reduction in thickness and subsequently subjected to prolonged ageing at 650 degrees C for 4000 h. The enhanced diffusion resulted in the decomposition of the Ni(2)(Mo,Cr) metastable phase into the stable Ni(3)Mo-based phase. The presence of the new stable phase increased the yield and tensile strengths but deteriorated the ductility of the alloy at both room and 650 degrees C temperatures.

Influence of tungsten on microstructure of mechanically alloyed gamma-TiAl.

This article presents preliminary results of the processing and characterization of gamma-TiAl alloy modified by W addition. An alloy with the target chemical composition of TiAl-5W (at.%) was synthesized by mechanical alloying. Two methods were used for powder compaction: hot pressing at 1300 degrees C and hot extrusion at 1100 degrees C. Hot extrusion turned out to be a superior consolidation technique over hot pressing. The matrix of final alloy was composed of a phase based on TiAl and a minor amount of Ti(3)Al. The grain size in the extruded alloy was much smaller than in the hot-pressed one. Minute W particles formed a dispersoid.