Metastable phases and macroheterogeneous composites

The way to control the interfacial reactions that processes during infiltration of macroheterogeneous composite materials is suggested. The idea is to combine the stable and metastable phases in the filler’s structure which dissolves at a different rate in the molten binder. To prove this approach, the structure and gas-abrasive wear of macroheterogeneous composite materials with Cu–20Ni–20Mn binder reinforced by Fe–(9.0–10.0)B–(0.01-0.2)C filler (in wt. %) cooled at 10–20 K/s or 103–104 K/s are studied. It is shown that the wear resistance of the investigated composite materials can be enhanced by accelerating interfacial reactions between the filler and the molten binder. Therefore, the composite materials produced from a rapidly cooled Fe–B–C filler show a higher resistance to gas-abrasive wear due to formation of Fe–Fe2(B,C) metastable eutectics in its structure. This eutectics crystallizes under metastable phase diagram due to the suppression of stable Fe2(B,C) phase formation and saturation of the rest of liquid by iron in the filler cooled at 103–104 K/s. As a result of rapid dissolution of the eutectics in the molten binder during infiltration, the strong adhesion at the interfaces of the composite materials is achieved which prevents the filler from spalling out under the impacts of abrasive.

Aging of the OT4-VT23, VT6-VT23, VT19-VT23 Titanium Welded Pairs

The structure, the phase composition and microhardness over the section of welded joints aged at 500 and 550 °C have been studied by means of structural and microdurometric analyzes. The welded joints of OT4-VT23, VT6-VT23 and VT19-VT23 titanium alloys pairs were obtained by the argon-arc welding with a nonconsumable tungsten electrode. It has been established that the aging at 500 °C for 8 hours promotes the decomposition of metastable phases (b, a”) which formed after welding in the welded joint of VT19-VT23 titanium alloys pair. The decomposition process leads to strengthening of the main zones of the welded joint (except for the parent metal of VT23 alloy) and provides a favorable smooth change of microhardness in the joint during the transition from one alloy to another. The aging at 500 and 550 °C during 8 hours of the welded joints of OT4-VT23, VT6-VT23 titanium alloys pairs also led to the development of the decomposition of metastable phases (b, a”, a’) in the weld and heat affected zones of the alloys being joined, but did not provide the required monotonic change in microhardness over the cross section of the joint.