| In conventional machining processing, cutting fluid is usually used to reduce friction and the wear. Although the use of cutting fluid can achieve the purposes of lubrication and cooling, it can cause environmental pollution problems in its storage, use and disposal process. Therefore, the research in manufacturing tends to focus on green manufacturing technology and the key technology to achieve green manufacturing is dry cutting. But the fast failure of dry cutting tools is still an important factor which restrict the development of machining technology. To solve this problem, many scholars continue to seek new cutting tool material, optimize tool structure and carry out studies on lubricating and cooling processes. Among them, nano-composite self-lubricating ceramic tool material has been proven to be effective to prolong tool life under dry cutting conditions.In this paper, focusing on the issue that the existing micron solid lubricant added self-lubricating ceramic tool does not take the mechanical properties and wear resistance into account, the addition of nano scale solid lubricants into ceramic tool is used to realize their self-lubricating properties. In this article, with the addition of micron TiB2 into submicron Al2O3 matrix as a reinforcing phase, an nano CaF2 as a solid lubricant, and by adjusting the volume proportion of matrix, enhancing phase and solid lubricant in nano composite ceramic tool material and optimizing the sintering process parameters, the Al2O3/TiB2/CaF2 nano composite ceramic tool material with good performance is ultimately prepared, and has been researched on its mechanical properties, microstructure. The main contents are as follows:(1) The determination to select TiB2 as toughening phase of composite ceramic tool materials, is based on its properties of high hardness, high melting point, high elastic modulus, high corrosion resistance, good thermal conductivity and thermal expansion coefficient and other excellent features. And the nano-CaF2 is choosed as the solid lubricant. This is based on the enhancing and toughening effect of nano-particles, then achieve the aim to avoid the performance degradation phenomenon of composite material which is due to the weakness of general solid lubricants in strength and hardness. The TiB2 and nano-CaF2 work together to toughen the matrix material and achieve its self-lubricating properties.(2) By deep study of the method to synthesize precipitation powder by chemical reaction, the calcium nitrate and ammonium fluoride were choosed as raw materials, and a composite of a solution of distilled water and ethanol as solvent, polyethylene glycol (molecular weight 6000) as a dispersing agent, preparing nano-CaF2 with a mean particle size of 20nm, and good monodisperse by direct precipitation method.(3) By the optimization of raw material components and multiple sets of experimental verifications, the volume ratio of Al2O3 and TiB2 is determined at 7:3, the volume fraction of CaF2 10%; and when the sintering process is as below: sintering temperature of 1550℃, holding time of 20min, sintered pressure of 30MPa, the mechanical properties of the prepared nano composite ceramic tool material is best.(4) The sintered Al2O3/TiB2/CaF2 self-lubricating ceramic material was prepared into sample, and the result of tests express as below:the hardness, flexural strength and fracture toughness of composite ceramic tool material were 16.5GPa,685MPa,3.6 MPa·m1/2. The surface morphology and fracture morphology of Al2O3/TiB2/CaF2 self-lubricating ceramic material were observed by scanning electron microscopy and its composition was determined by XRD, and the XRD indicates there was no chemical reaction between Al2O3, TiB2, CaF2.(5) By using a pin-disc Vice forms of Al2O3/TiB2、Al2O3/TiB2/5%CaF2、 Al2O3/TiB2/10%CaF2, friction wear tests are performed. The results showed that, the wear of Al2O3/TiB2 is a typical abrasive wear, its coefficient of friction is large; the surface of Al2O3/TiB2/5%CaF2 begin to form a lubricating film with different sizes, by addiction of nano CaF2 into composite ceramic material, the form of friction is changed, then further reducing the friction coefficient; Al2O3/TiB2/10%CaF2 self-lubricating ceramic material can form a more complete lubricating film on the wear face, this can meet self-lubricating properties. |
PDF Full Text Request