FORMATION BY MECHANICAL ALLOYING Ti-Al COATINGS WITH COBALT AND NICKEL ADDITIVES

The work is dedicated to the formation of TiAl titanium aluminide coatings with cobalt and nickel additives by means of the method of mechanical alloying with the further maturing at high temperature in vacuum. Coatings were applied with the use of the ball mill of the planetary type upon VT1-0 titanium alloy substrate which were placed in the mill cup filled with metal powders. There is studied growth kinetics, a coating thickness is measured. A specific rate of metal powder sedimentation upon a titanium substrate makes from 4.6 to 11 g/(min•m2). Deposited layers have a mean thickness 70-180 mkm. There are studied thoroughly compositions and microstructure of mechanical-alloyed coatings. For that there were used methods of X-ray diffractometry and raster electronic microscopy. It is defined that the inner structure of coatings is heterogeneous. After deposited layer thermal treatment a metal interpenetration takes place first aluminum into particles of titanium, cobalt or nickel. Coatings are composite material the basis of which makes aluminide of RiAl titanium, and as inclusions there are other inter-metallides, titanium, cobalt or nickel and also aluminum oxide. Mean values of micro-hardness of coatings obtained are 1.2 - 3.4 times higher than of titanium substrate. The highest values of micro-hardness (more than 6.5 GΠa) after thermal treatment in vacuum are observed in TiAl-5%Co and TiAl-10%Co coatings. Micro-hardness of VT1-0 titanium alloy after annealing, vice versa, decreases by 1.3 times.

OXIDATION KINETIC AND ANODIC BEHAVIOR OF Zn22Al ALLOY DOPED WITH NICKEL

The article presents the results of the study of the oxidation kinetics and the anodic behavior of the zinc-aluminum alloy Zn22Al, doped with nickel, in various corrosive environments. The kinetic and energy parameters of the process of high-temperature oxidation of alloys are determined. It is shown that the process of high-temperature oxidation of samples of Zn22Al-Ni alloys is characterized by a monotonic decrease in the true oxidation rate and an increase in the effective activation energy at the content of the alloying component in the initial Zn0.5Al alloy up to 0.5 wt.%. It was found that nickel additives within the studied concentration (0.01-0.5 wt.% ) slightly increases the oxidability of the base alloy Zn22Al at temperatures of 523, 573 and 623 K. It is shown that the dependence of the corrosion potential of zinc-aluminum alloys on the nickel content in them is of the same type, i.e. the additives of the alloying component contribute to the displacement of the corrosion potential in the region of positive values. The influence of the aggressiveness of the corrosive medium on the anodic behavior of alloys when comparing concentrated electrolytes with the increasing concentration of chloride ions in the sodium chloride solution is established. It is determined that the potentials of pitting formation and repassivation of the initial alloys shift to a more positive region with an increase in the nickel concentration in the alloys. The greatest shift of these potentials to the positive region is observed when alloying alloys containing small nickel additives. It is shown that the corrosion products of the studied alloys consist of a mixture of protective oxide films Al2O3, ZnO, NiO, Al2O3·ZnO and Al2O3·Ni2O3. It was found that the alloying of zinc-aluminum alloys with nickel (in the range of 0.01–0.05 wt.%) reduces the corrosion rate of the base alloy by 2-3 times. The proposed alloy compositions can be used as an anode coating for corrosion protection of steel products and structures.

Thermal Hardening of the Tin Bronze Alloyed with Nickel

The article represents the results of thermal hardening of the stannic bronze alloyed with nickel without quenching. The samples were obtained by molding into a metal form applying centrifugal way of molding. Metallographic and phase analyses were carried out to define the mechanism of thermal hardening. The aging mode was chosen to ensure the maximum hardness of stannic bronze with nickel additives of the chosen structure.