Alexander Laptev

Study of production route for titanium parts combining very high porosity and complex shape

Abstract The production of highly porous titanium parts of complex shape by powder metallurgical technology is described. Well defined porosity and pore sizes were achieved using a pore forming additive. This additive also enhances the strength of unsintered compacts, allowing machining in the green state. The requirements of the initial powders and pecularities of each production step are discussed in detail. The microstructure of porous materials and examples of net shape parts are given, aiming preferentially at biomedical applications. The impurities of the obtained titanium parts are compared with the requirements of the ISO standard for titanium implants.

Green strength of powder compacts provided for production of highly porous titanium parts

Abstract The production route of highly porous near net shape titanium parts includes the green machining of compacts made of metallic and pore former (often ammonium bicarbonate) powder mixtures. Success in green machining greatly depends on compact strength. The aim of the present work was to determine and quantitatively evaluate factors influencing the green strength of titanium–ammonium bicarbonate compacts. The substantial dependence of green strength on the amount of pore former and compaction pressure was demonstrated. Some influence of the particle size of ammonium bicarbonate on compact strength was also observed. A theoretical explanation of these experimental results is given. A sharp decrease of green strength owing to decomposition of ammonium bicarbonate in compacts during holding in air was experimentally found. The factors influencing decomposition, i.e. time, compaction pressure and particle size of pore former, were investigated in detail. The catalytic action of titanium on decomposition of ammonium bicarbonate is discussed.

Microstructure and mechanical properties of spark plasma sintered ZrO2-Al2O3-TiC0.5N0.5 nanocomposites

Future materials for wear resistant components require a combination of excellent mechanical properties such as hardness and toughness, short processing times and good electrical conductivity to facilitate shaping by electro discharge machining (EDM). In this work, the hardness and fracture toughness of t-ZrO2 based electro conductive composites was optimised, while short processing times below 20 minutes using spark plasma sintering were sufficient to obtain near fully dense materials. The influence of powder processing technique using TiC0.5N0.5 as the starting powder and yttria as a stabiliser on the mechanical properties of ZrO2-TiC0.5N0.5-Al2O3 based composites was investigated. Fully dense Y-TZP based composites possessed an excellent toughness of 9.2 MPa.m1/2 and an increased Vickers hardness of 1397 kg/mm².

Review of the Powder Metallurgical Production of Net-Shaped Titanium Implants

The paper gives a short review of P/M routes which were developed or adapted by the authors for the net-shape manufacturing of titanium implants. Special attention is paid to the production of highly porous bone implants, where the porosity is achieved by the application of temporary space holder particles, which are removed before or during sintering by decomposition or dissolution. In this case, shaping was done either by machining of powder compacts in the green and sintered state or by metal injection moulding (MIM). The challenges of these shaping technologies and current solutions are discussed. To complete the review, two promising new technologies for the net-shape production of highly porous titanium implants, the replica technique and additive manufacturing are briefly introduced.