Study On Fabrication, Characterization And Tribological Properties Of High Temperature Self-Lubrication Metal Ceramics With Sweat Gland Structure

As a new self-lubricating technology,the high temperature sweating selflubrication is put forward based on human's sweat-gland structure and its sweating mechanisms.Its materials are composed of hard phase of metal ceramics with sweatgland structure and soft phase of multi-element solid lubricants.The mechanism of self-lubrication is that the lubricants deposited in the composites were diffused out to the friction interface through orderly pore channels of the composites with sweatgland structure.The research project has been supported financially by National Natural Science Foundation of P.R.China.Research status and developing trends of porous materials,high temperature solid self-lubrication composites and biomimetic structural materials were reviewed in this dissertation.A new concept of high temperature sweating self-lubrication was brought forward.Using a two-time pore-forming method,a metal ceramic preform with sweat-gland structure was fabricated by powder metallurgy method. Subsequently,a new type high temperature sweating self-lubrication metal ceramics was manufactured successfully through infiltrating molten solid lubricants into the preforms in vacuum.The design theories,micro structure,tribological characteristics and self-lubricating mechanisms were were analyzed systemtically.For achieving ordering array of the micropores on the surface and the inner interpenetration of sweat gland structure micro pores,a micro-pore model describing the characteristics of the sweat gland structural micro pores was established through structural and functional imitation of human' sweat-gland structure.Based on the study of pore evolution during the powder metallurgy sintering process,the model was statistical approach analyzed.Subsequently,mechanisms for controlling poreshape, pore-structure and pore-size distribution were developed.To control both the pore structure and the toughness of sweat-gland structural sinteres,besides the tribological design of the composition of composite matrix,a compound pore-forming agent,TiH₂ and CaCO₃,which can decompose sequentially was made.Fine Al₂O₃ particles were included as dispersion.A new solid-liquid sintering technology through two-time pore forming method was innovated.As a result,strong sinters with a sweat gland structure and interconnected and uniformly opened micro-pores on the surface were fabricated.For achieving high temperature self-lubrication properties of metal ceramics with sweat gland structure,a compound solid lubricants composed of lead,tin,silver and rare earth elements was created based on the characteristics of self-lubrication film forming process,difference in the melting points and wettability of soft metal solid lubricants.The compound solid lubricants were infiltrated into high intensity sinters with sweat gland structure using high pressure infiltrating method in vacuum. Metal ceramic composites fabricated through this method possess good high temperature self-lubrication properties.Using TiC-FeCrWMoV high temperature self-lubrication metal ceramics with sweat gland structure as the representative objective,the characteristics of the pore structure,mechanical properties and tribological properties were investigated microscopically.The experimental studies and the theoretical analysis reveal that the metal ceramics have homogeneous regular pores as well as a narrower pore size distribution and high pore connectivity.The pore size distribution was approximately fitted by the Rayleigh distribution curve.These materials where both solid lubricant phase and matrix phase were interpenetrating throughout the microstructure possessed high intensity,fine wear resistance and a good self-lubrication properties (at 600℃,the average friction coefficient ranging from 0.26 to 0.29 and the wear rate ranging from 6.3×10^-6～9.6×10^-6mm³/Nm).By means of energy dispersive X-ray analysis(EDX)and X-ray diffraction (XRD),it was found that the lubricating elements were diffused or squeezed out of the matrix,forming a thin lubricating film consisting of lead,tin,silver,copper et al on the friction surface.A model for describing the forming process of solid lubricating film was established based on the analysis of SEM topography.The mechanism of self-lubrication of the high temperature sweating self-lubrication composites with sweat gland structure was studied.