Formation mechanisms of Ni-Al intermetallics during heat treatment of Ni coating on 6061 Al substrate

The formation mechanisms and growth kinetics of Al3 Ni and Al3Ni2 in Ni-Al diffusion couple prepared by electrodeposition of Ni on Al substrate were investigated. The nickel coating with 20 μm thickness was applied on 6061 aluminum alloy by direct current electroplating. The samples were then heat-treated for different durations at 450, 500 and 550 °C under argon atmosphere. The intermetallic phases were identified by means of scanning electron microscopy（SEM）, energy dispersive spectrometry（EDS） and X-ray diffraction（XRD）. The results showed that the formation of intermetallic phases consisted of two important steps. The first step was the lateral growth of intermetallic phase from separate sites, resulting in the formation of a continuous layer. The second step was the growth of the continuous intermetallic layer in the direction perpendicular to the interface. However, excessive increase in thickness of intermetallic phases led to the detachment of reaction products, i.e., Al3 Ni and Al3Ni2, from the substrate. It was also observed that aluminum was the dominant diffusing element during Al3 Ni growth, while nickel diffusion was dominant during Al3Ni2 growth. The growth kinetics of both Al3 Ni and Al3Ni2 phases obeyed a parabolic law.

Transient liquid phase bonding of Al 2024 to Ti-6Al-4V alloy using Cu-Zn interlayer

Transient liquid phase bonding of two dissimilar alloys Al 2024 and Ti?6Al?4V using Cu?22%Zn interlayer was carried out at 510 °C under vacuum of 0.01 Pa for various bonding time. In order to characterize the microstructure evolution in the joint zone, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied. The results show that joint formation is attributed to the solid-state diffusion of Cu and Zn into Ti?6Al?4V and Al 2024 alloys followed by eutectic formation and isothermal solidification along the Cu?Zn/Al 2024 interface. The hardness of the joints at the interface increases with an increase in bonding time which can be attributed to formation of intermetallic compounds such as Al2Cu, TiCu3, Al4.2Cu3.2Zn0.7, Al0.71Zn0.29, Ti2Cu, TiAl3 and TiZn16 in the joint zone. Moreover, shear strength of the joint reaches the highest value of 37 MPa at bonding time of 60 min.

Electrodeposition mechanism of Ni-Al composite coating

Ni-Al composite coatings were electrodeposited from a modified Watts solution. The electrochemical behavior of the coatings was studied by means of zeta potential analysis, voltammetry and electrochemical impedance spectroscopy（EIS）. It was found that the zeta potential of Al particles was-4 m V which is very close to that of Al2O3. Moreover, addition of conductive Al particles into the electrolyte shifted the polarization curve to more negative potentials and loop size of EIS curve increased. It was also demonstrated that the co-deposition behavior of Ni-Al composite coatings obeys the Guglielmi’s model. The results indicate that conductive Al particles behave as the inert particles and confirm the existence of a thin aluminum oxide layer on the surface of aluminum particles.

Microstructure and wear behavior of AA6061/SiC surface composite fabricated via friction stir processing with different pins and passes

In this investigation,the effects of pin geometry and number of passes on macrostructure,microstructure,wear rate and also microhardness profile of 6061-T6 aluminum alloy surface composites fabricated via friction stir processing(FSP)were discussed by reinforcement particles of silicon carbide(SiC).The results show that after each FSP pass,a modify distribution of SiC particles is acquired and the increase in the number of passes reduces the average grain size in stir zone(SZ).Furthermore,it is discovered that pin geometry and pass number play a dominant role in the grain size of SZ and distribution of SiC particles in SZ.It is found that after each FSP pass,wear rate is improved due to the uniform distribution of SiC particles in surface of Al/SiC composite.Additionally,the results show that the square pin and smooth(straight)cylindrical pin have the highest and lowest resistance to wear,respectively.

Structural and Mechanical Properties of TiN-TiC-TiO System: First Principle Study

Mechanical and structural properties of ternary system of TiN-TiO-TiC are investigated using first principle methods. 70 different compositions of Ti100(NOC)100 with cubic structure are examined in order to illustrate the trend of properties variations. The geometry of compounds is optimized, and then, their chemical stability is assessed. Afterward,shear, bulk and young moduli, Cauchy pressure, Zener ratio, hardness and H3/E2 ratio are computed based on elastic constants. Graphical ternary diagram is used to represent the trend of such properties when the content of nitrogen,oxygen and carbon varies. The results show that incorporation of oxygen into the system decreases the hardness and H^3/E^2 ratio while subsequently ductility increases due to positive Cauchy pressure. It is revealed that the maximum H^3/E^2 ratio occurs when both nitrogen and carbon with a little amount of oxygen are incorporated. Ti_(100) N_(30) C_(70) owns the highest hardness and H^3/E^2 ratio equal to 39.5 and 0.2 GPa, respectively. In addition, the G/B of this compound,which is about 0.9, shows it is brittle. It is also observed that the solid solutions have better mechanical properties with respect to titanium nitride and titanium carbide. The obtained results could be used to enhance monolayer coatings as well as to design multilayers with specific mechanical properties.