N.K Tolochko

Absorptance of powder materials suitable for laser sintering

The normal spectral absorptance of a number of metal, ceramic and polymer powders susceptible to be utilised for selective laser sintering (SLS) technique was experimentally determined. The measurements were performed with two laser wavelengths of 1.06μm and 10.6μm obtained by using two lasers – Nd‐YAG and CO2 respectively. The change in the powder absorptance with time during laser processing was also investigated. The effect of the absorptance characteristics on the sintering process is discussed.

Balling processes during selective laser treatment of powders

The particularities of the selective laser processing of single‐component metal powder layers were investigated, especially the occurrence of the balling‐processes under different processing conditions. During laser processing, sintered, semi‐sintered/semi‐melted or completely melted cakes can be formed. Size and shape of the laser processed parts can change depending on the energy and time parameters of the laser irradiation and on the properties of initial powder layers.

Mechanisms of selective laser sintering and heat transfer in Ti powder

Coupled metallographic examination and heat transfer numerical simulation are applied to reveal the laser sintering mechanisms of Ti powder of 63‐315 μm particle diameter. A Nd:YAG laser beam with a diameter of 2.7‐5.3 mm and a power of 10‐100 W is focused on a bed of loose Ti powder for 10 s in vacuum. The numerical simulation indicates that a nearly hemispherical temperature front propagates from the laser spot. In the region of α‐Ti just behind the front, heat transfer is governed by thermal radiation. The balling effect, formation of melt droplets, is not observed because the temperature increases gradually and the melt appears inside initially sintered powder which resists the surface tension of the melt.

Selective laser sintering of single- and two-component metal powders

A comparative characterisation of selective laser sintering (SLS) mechanisms of single‐ and two‐component powders is presented. The effects of the volume fraction of liquid phase and the powder absorptance were discussed. Single‐component Ni‐alloy, Fe and Cu powders as well as two‐component powder systems based on Ni‐alloy, Fe and Cu were investigated. In particular, the following types of two‐component powder systems were studied: Ni‐alloy‐Cu and Fe‐Cu powder mixtures as well as Cu‐coated Ni‐alloy powder and Cu‐coated Fe powders. SLS experiments were performed with a CW‐ Nd:YAG laser (λ=1.06 μm). The acting mechanism in all cases was liquid phase sintering.

Dental root implants produced by the combined selective laser sintering/melting of titanium powders

Abstract Preliminary experiments were carried out for the fabrication of dental root implants using an improved technique of laser processing of Ti powders. The properties of produced samples were characterized for various processing parameters. Samples with rod and cone shapes were formed. A combined selective laser sintering (SLS) and selective laser melting (SLM) process was utilized. With this combination, the samples possessed a structure composed of two different zones, namely a remelted compact core and a sintered porous shell. The results of these experiments show that it is possible to produce dental root implants possessing the required geometry, structure and strength by appropriate laser processing of Ti powder.

Bone osseointegration tests performed on titanium dental root implants made by laser processing

Bone in-growth tests were performed on dental root implants fabricated using an improved technique of laser processing of Ti powders. This technique consists of combined laser-sintering/laser-melting processes. Through this combination, implant samples were made possessing a structure composed of two different zones, namely a remelted compact core and a sintered porous shell/layer. The laser-processed implants were then inserted into the lower jawbone of a dog for bone osseointegration analysis. The results of this investigation show that it is possible to produce dental root implants possessing the required geometry, structure and strength that might be suitable for medical applications.

Selective laser sintering of compacted powders

The selective laser sintering of preliminarily compacted powders was investigated. Depths of sintering lower than those with freely poured powders were attained. This has a negative effect on the production of multilayered articles. The main disadvantage of the process, however, was the difficulty in separating the article from the unsintered compacted powder.

Experimental investigation of the kinetics of regrouping and zonal isolation of particles in the laser sintering of a monolayer of one-component metallic powder

The laws of particle regrouping in the laser sintering of a one-component metallic powder were experimentally investigated. The main features of zonal isolation were studied. Spherical particles arranged in a monolayer were subjected to laser sintering. The variation of porosity and average number of interparticle contacts in the monolayer with time were investigated under different conditions of initial particle distribution.

Kinetics of interparticle contact formation during the laser sintering of two-component powders

The kinetics of interparticle contacts formation during the liquid-phase sintering of unlike materials under the action of laser irradiation was investigated. Trios of particles arranged in a row according to the schemes glass—polymer glass, metal—polymer—metal, and metal—glass—metal were sintered. The processes of particle approach and liquid neck formation between particles were studied. Possibilities for the manufacture of powder components with polymer and glass binders by the use of selective laser sintering followed by heat treatment are considered].