Laser surface polishing of Ti-6Al-4V parts manufactured by laser powder bed fusion

Poor surface quality of Additively Manufactured (AM) components, can greatly increase the overall cost and lead time of high-performance components. Examples are medical devices where surfaces may contact the patient’s skin and hence need to be smooth and aerospace components with high fatigue strength requirements where surface roughness could reduce fatigue life. The average surface roughness (Ra) of AM parts can reach high levels greater than 50 microns and maximum distance between the high peaks and the low valleys of more than 300 microns. As such, there is a need for fast, cost effective and selective finishing methods of AM produced components targeted at high-performance industries. In this paper Ti-6Al-4V Grade 23 ELI, popular for medical devices and aerospace parts production, was L-PBF processed to manufacture parts which were subsequently treated via laser polishing. Here in this work, CO2 laser polishing was used for the surface modification of the Ti-6Al-4V produced samples. The most significant processing parameters were optimised to achieve approximately an 80% reduction in the average surface roughness and a 90% reduction in the peak-to-valley distance with a processing time of 0.1 sec/mm2 and cost of 0.2 €/cm2

Effects of powder compression and laser re-melting on the microstructure and mechanical properties of additively manufactured parts in laser-powder bed fusion

Achieving good surface profile and low levels of porosity are prime challenges in the Laser-Powder Bed Fusion (L-PBF) additive manufacturing technique. In order to optimise these properties, post-processing is often required. However, the compression of powder spread on the build plate and re-melting of each build layer during the L-PBF process could address these challenges. In this study, the effect of different powder compression ratios and laser re-melting regimes on the density, microstructure morphology, surface profile and mechanical properties of L-PBF produced parts were investigated. Two different metal printers with same laser processing parameters were used to fabricate 10 x 10 x 10 mm3 stainless steel 316L samples. To examine the impact of compression ratio and layer re-melting, one set of samples was prepared with three different compression levels for each layer, and the second set of samples either a single or double set of laser passes for each layer. The Volumetric Energy Density (VED) range examines was from 26.7 J/mm3 to 80 J/mm3. Density, hardness, elastic modulus, microstructure, and surface profiles of the printed samples were characterized. A 3% increment in density and a 50% reduction in the surface roughness were achieved using a laser double pass over each layer. The results demonstrate, by applying different powder compression ratios onto the powder bed and by re-melting each layer, that the density, surface roughness, and the elastic modulus of the produced samples can be improved

Ti-6Al-4V alaşımının 3 boyutlu elektron demeti ergitme yöntemiyle üretilmesi ve ikincil işlemlerin geliştirilmesi.

In this thesis, the effects of production variables in electron beam melting (EBM) and post-processing on the materials’ and mechanical properties of Ti-6Al-4V alloy were investigated by considering the microstructural change. Ti-alloy samples were produced at 0o, 45o and 90o with respect to building plate. Surface polishing with HF solution was applied to reduce the surface roughness. On the other hand, post-heat treatments, namely, 2-step thermo-hydrogen processing (THP) and annealing, were conducted to improve the mechanical properties, i.e. hardness and tensile strength, and to increase fatigue life. Production at different angles had no influence on texture formation such that in all samples the texture of α-phase was commonly concentrated in (101 ̅0) plane, which was parallel to building direction. The samples produced at 0o had the coarsest and lowest microstructure and hardness value, respectively, possibly due to higher heat input during production; however, they possessed comparatively higher density and lower surface roughness. Therefore, the samples displayed high tensile strength and ductility comparable to standards. Likewise, fatigue life improved by production at 0o due to lower surface roughness and defects. THP refined the microstructure and slightly increased the hardness by altering the texture. Although tensile strength increased, ductility reduced possibly due to oxidation. Annealing coarsened the microstructure and degraded the mechanical properties. On the other hand, both post heat treatment processes did not influence the fatigue life due to predominant effect of high surface roughness. Despite the reduced surface roughness by surface polishing, fatigue life decreased because of dissolved hydrogen in samples.Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Metallurgical and Materials Engineering

Üç Boyutlu Elektron Demeti Eritme (EDE) Yöntemiyle Üretilen Ti-6Al-4V Alaşım Parçalarının Mekanik Özelliklerinin ve İçyapısının İkincil İşlemlerle Geliştirilmesi

Katmanlı imalat yöntemi 1990’ların başlarında metal alaşımların hızlı prototiplenmesinde kullanılmaya başlanmıştır. Çeşitli mühendislik alanlarının üretim kabiliyetini arttırması beklenen bu imalat yöntemi, konvansiyonel metal şekillendirme yöntemlerinin sınırlandırdığı sektörlerin gelişmesine katkı sağlayacaktır. Ancak, katmanlı imalat ile üretilen alaşımlardaki kalıntı gerilimine bağlı düşük süneklik, kalıntı gözenek ve kaba mikroyapı gibi mekanik özelliklere direkt olarak olumsuz etki eden unsurlar bu üretim yöntemi ile üretilen parçaların yük taşıyan uygulamalarda kullanımını kısıtlamaktadır. Dolayısıyla, katmanlı imalat ile üretilmiş alaşımların geometrilerini bozmadan mikroyapılarını ıslah edecek ikincil proseslere ihtiyaç bulunmaktadır. Son yıllarda yapılan çalışmalarda hidrojen gazı etkileşimi ile uygulanan ısıl-hidrojen işlemlerin titanyum alaşımlarının iç-yapısını düzenleyerek mekanik özelliklerini geliştirdiği ortaya konmuştur. Önerilen projede katmanlı imalat metodlarından biri olan elektron demeti eritme (EDE) yöntemiyle üretilen Ti-6Al-4V alaşımına yüksek sıcaklıkta hidrojen gazı emdirilip tekrar yapıdan alınarak (ısıl-hidrojen işlemi) malzemenin şekli bozulmadan yapıda mikro boyutlarda değişimler yaratılıp mekanik özellikler geliştirilecektir. Proje sonucunda, ısıl-hidrojen işlemi sayesinde EDE ile üretilen Ti-6Al-4V alaşımlarına uygulanan klasik tavlama işlemlerinin aksine kalıntı geriliminin azaltılarak sünekliğin ve dayancın arttırılması hedeflenmektedir

Property Development of EBM Processed Ti-6Al-4V Alloy Through Hydrogen Treatments

Ti-6Al-4V alloy attracts attention as the most preferred material in defense and aviation-space industries due to its low density, high specific strength and corrosion resistance as well as its high fatigue strength. In contrast to conventional techniques, production of very complex shaped Ti-alloys is possible at a single step using additive manufacturing (AM) techniques which also allow energy and time saving. Among these techniques, Electron Beam Melting (EBM) technique is capable of producing parts with relative densities over 99% with comparatively low residual stresses. However, a high temperature postprocess annealing heat treatment is inevitable to increase the ductility of the EBM manufactured component. The decrease in strength, possibility of distortion and microstructural coarsening are some of the drawbacks of such annealing processes. For this reason, in the present study, thermo-hydrogen treatment is used as an alternative post-process heat treatment for microstructural refinement, residual stress reduction and ductility improvement in EBM manufactured Ti-6Al-4V alloy parts without degrading the strength of the alloy. For this purpose, EBM manufactured samples were hydrogenated and dehydrogenated between 600 and 800 qC under Ar-H2 gas mixture atmosphere and high vacuum, respectively. Microstructural refinement and phase changes during the thermo-hydrogen treatment were characterized, and the effect of the thermo-hydrogen process on the mechanical properties was observed using micro-hardness tests

High strength bioinspired calcium phosphate-based material for bone repair applications

Owing to the increasing demand for bone repair strategies, several biomaterials have been developed. Among the materials available for this purpose, hydroxyapatite stands out for its osteoinduction capacity, since it possesses a chemical composition similar to that of inorganic bone constituents. In comparison to bones, the mechanical properties of substitute structures incorporating hydroxyapatite still remain a great challenge for scientists. This study thus presents the synthesis of hydroxyapatite incorporated with a natural bioceramic and a metallic phase of excellent biocompatibility to obtain dense biomaterials with improved mechanical strength. The mechanical responses of the synthesized biomaterials are presented and discussed. The results obtained indicate that the hydroxyapatite-natural ceramic systems fulfils the general mechanical property requirements for some bone repair applications. Separately, the synthesis of titanium-based systems was shown to be much more challenging, but promising. Therefore, recommendations for suppressing the issues with the metal-ceramic interfacial bonding strength were provided

A comprehensive characterization of the effect of spatter powder on IN939 parts fabricated by laser powder bed fusion

This study is focused on a comprehensive characterization of virgin and spatter IN939 powders and the effects of a certain amount of spatter powder on the part quality of IN939 fabricated by the L-PBF process. A brown tint coloration formed Al2O3 oxide, pores, a 124.4% increase in the average particle size, a 10.2% decrease in the powder circularity, and a 7.5% decrease in the powder aspect ratio were observed in the spatter powder. Additionally, higher average grain size and lower nanohardness were obtained for the spatter powder. In order to understand the effect of a certain amount of spatter powder on the part quality, 10 wt% spatter powder was mixed with the virgin powder. This addition was found to decrease the flowability of the powder. Moreover, this addition decreased relative density by around 0.3% and increased surface roughness by around 80.8% in the fabricated samples (termed as V and SV). On the other hand, there was no considerable microstructural, texture, microhardness, and nanohardness difference between V and SV samples, although the spatter powder addition caused a 30.2% increase in the average grain size of SV. The overall texture for both V and SV samples exhibit (0 0 1)//BD.</p