Novel Application Of Ultrasonic Cavitation For The Fabrication Of TiN_p/Al Composites And Its Properties

The characteristics of particulate reinforced aluminum matrix composites(AMCs)are excellent in specific modulus,specific strength and wear resistance,so they are expected to be promising materials in the field of automobile and high-speed railway industries.Nevertheless,the production of Ti N particulate and Ti N particulate reinforced AMCs by casting process have some difficulties due to a number of reasons.The wettability between Ti N and the Al melt is very poor(the contact angle 135° @ 900 ?),which makes the incorporation,retention and dispersion of the smaller Ti N particles in the Al melt extremely difficult.This situation is becoming even worse when the particle size decreases.Ultrasonic cavitation has been considered as a new,powerful and economical ceramic powders and aluminum matrix composites fabrication technology.Two main research interests are included in this paper.The first is the effectsand mechanism of ultrasonic cavitation on the porous Ti N particles in both water and Al melt.The other is the application of ultrasonic cavitation for the fabrication of Ti Np/Al composites and its properties.The Large polycrystalline Ti N particles with porous structure(average particle size of 264 ?m and mean pore diameter of 4 ?m)produced from direct nitriding metal Ti in industry have the same microstructure of the as-received sponge Ti.A microscope system was utilized to verify and observe the cavitation bubbles,whichformed and collapsed repeatedly on the surface of porous Ti N particles.The single particle crushing test shows that the strength of the porous Ti N particles increased with the decrease of particles size.The strength of the porous Ti N particles is in the range of 42-122 MPa.The effects of ultrasonic treatment time,ultrasonic intensity,solids concentration and liquid volume on the kinetics of comminution process of Ti N in water weresystematacially studied.The porous Ti N particles was decreased to the particle size of 10-30 ? m with an ultrasonic intensity of 11,29,33W/cm2.A mass of sub-micro Ti N particles were also produced and well dispersed in water with prolongedultrasonictreatment.The time of the comminution process of porous decreased with and increase of ultrasonic intensity.The contents of the porous Ti N particles(2.5 g-10 g)and the volume of the water(250 ml-500 ml)have little effect on the comminution process of porous Ti N.Porous Ti N particles were effectively incorporated into Al melt.Ultrasonic treatment with an ultrasonic intensity of 59W/cm2 wasable to comminuteporous Ti N particles and dispersion of produced fine Ti N particles(average particle size of 15 ?m)in Al melt.ANSYS finite element platform was applied to calculate the ultrasonic pressure distribution and amplitude along the axis of the vibrating surface of the horn in the above different ultrasonic treatment systems.The result was that when the ration was greater than 10,the shock waves and microjects induced by the well-developed ultrasonic cavitationcan lead to the intergranular fracture of porous Ti N particles and the pitting of the surface of Ti N particles.Base on the results of ultrasonic cavitation on the porous Ti N particles and its mechanism in water and Al melt,a simple and econimical casting technology for a convenient fabrication of Ti Np/Al(CP Al,A356 and Al-5Cu)composites via ultrasonic cavitation was conceived.The average mass fraction and granular size of the Ti N particles inthe Ti N particulate reinforced AMCsare about 12% and 15 ?m,respectively.Microstructural characterization showed that the produced Ti N particles were much smaller than the porous Ti N particles and distributed uniformly in the matrix.XRD,SEM,EDS line scan and TEM revealed that the fine Ti N particles were stable during the process and had a clean and smooth interface with the Al matrix.The grain sizes of all thematrix were refined considerably by the fine Ti N particles.The hardness and tensile properties of the Ti N particulate reinforced AMCs at ambient temperature were also improved.Dry sliding friction test showed that the coefficients of friction of the Ti N particulate reinforced AMCs were more stable and lower than the Al matrix.The wear resistance of Ti N particulate reinforced AMCs is better than that of Al matrix due to the fine Ti N particles reinforced and pinned on the sliding surface.The wear volume increased with increase in applied load for the matrix and the Ti N particulate reinforced AMCs.