Oana Gîngu

Bulk titanium for structural and biomedical applications obtaining by spark plasma sintering (SPS) from titanium hydride powder

Titanium is a low density element with excellent mechanical properties, and is an attractive material for structural and biomedical applications. In recent years, a new process technology is emerging by which titanium and titanium alloys can be obtained by using titanium hydride (TiH2) as a precursor for Ti and its mixture with alloying elements. The feasibility of this manufacturing approach has been fully demonstrated from powder to sintering and from microstructure to mechanical properties. In this paper, a study concerning powder metallurgy processing of Ti by spark plasma sintering (SPS) route is presented. The influence of the technological parameters on the hardness and microstructures change during SPS has been studied. The experimental results are related to microscopic, thermal, and mechanical analysis.

Research of the Milling Time Influence on Ag-Cu Powder Particles Size Processed by Mechanical Alloying Route

This research focuses on Ag-Cu powder particles processing by mechanical alloying (MA) route. The powder mixture is representative for the eutectic composition, respectively 72%wt. Ag + 28% wt. Cu. The milling process is developed in high energy ball mill Pulverisette 6, using different size for the milling balls, in wet conditions for 80 hours. One of the most important parameter studied in this research is the particle size distribution of the processed powder mixture. Thus, it changes along the milling time, from 10…75 µm at the beginning of MA process up to (60 – 80) nm at 80 h. The milling parameters will be optimized in future research depending on the particle size distribution related with thermophysical and thermodynamic properties focused on electrical and optical properties improvement.

Influence of the Reinforcing Elements on the Wear Behavior of Al/(Sic+Graphite) Composites Elaborated by Spark Plasma Sintering Technology

The paper presents the experimental results regarding the influence of the reinforcing elements on the wear behavior of Al-matrix composites discontinuously reinforced by SiC and Graphite. This antifriction composite material is processed by Reactive Mechanically Alloyed and then by Spark Plasma Sintering technology. In order to optimize the processing technology, especially the sintering parameters, the Spark Plasma Sintering process was applied because of its advantageous aspects: lower sintering temperatures, shorter sintering time and higher properties values of the sintered material vs. the corresponding ones obtained by the classical sintering route. The authors realized a comparative analysis on the wear behavior of the researched composite materials.

New Injection Moulding Techniques for Automotive Aluminium-Based Foams - Part I

The raw material to be compacted by moulding is represented by aluminium alloy (ALUMIX 321) powder particles as metallic matrix and carbamide as foaming agent. The raw material to be injected is represented by the mixture (feedstock) between the wax-based binder system (40-60% mass) and the aluminium alloy (ALUMIX 321) powder particles (balance). The binder system is made of paraffin wax and stearic acid. The foaming effect is generated by addition of carbamide as foaming agent. Both categories of raw samples were washed in the ultrasonic machine and the aim of research was to study the physical properties and the macroscopic analysis of this materials.

Finite Element Analysis of a Lumbar Vertebra Reconstructed by Biocomposite Alloplastic Grafts

This research approaches the fourth lumbar (L4) vertebra reconstruction by a tronconic alloplastic graft fabricated by a powder metallurgy technology using Ca5(PO4)3(OH) (hydroxyapatite), TiH2 (titanium hydride) and CaCO3 (calcium carbonate) particles as initial powder mixture. The high frequency of the L4 vertebra fractures due to motor vehicle traffic accidents justify the necessity of vertebral reconstruction. This approach simulates the biomechanical behavior of the ANSYS model consisting in the L4 vertebra and the tronconic biocomposite graft during the frontal impact load. The von Misses stress and strain responses from the model depend on the physical and mechanical properties of the biocomposite grafts, experimentally determined. The best simulated mechanical behavior corresponds to the mechanical shielding phenomenon occurring from the biocomposite graft on behalf of the L4 vertebra.

Obtaining of Biopolymer from Onion Used as a Binder in Powder Injection Molding Process

The very important strategy in parts processing by powder injection molding (PIM) technology is the use of organic polymeric materials made from raw and auxiliary materials and from renewable natural sources. Using natural polymers to obtain binders for PIM use is of particular interest. The inulin extraction from the onion bulbs has a major alternative in this area.

Morphological and Thermophysical Behavior of Hidroxyapatite Powders Processed by Mechanical Milling

The current research represents one section of our studies concerning the improvement of the biocompatibility related to the biocomposite materials for bone grafts application. The submicronic/nanometric hydroxyapatite stands for the progress in biocompatibility. This study highlights the wet mechanical milling process and its effects on the morphological and thermophysical properties of the hydroxyapatite powder particles (30-50µm as raw material) obtained by this method (500 nm average). The scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) facility point out the morphological and chemical compositional features of the processed powders during 10 hours in dry argon atmosphere. The thermal analysis (TA) in argon atmosphere, too, reveals the influence of the milling parameters on the thermal effects generated by the processed hydroxyapatite powders. The experimental results of our research validate some milling mechanisms reported by the literature for wet/dry mechanochemical process conditions.

Research about the Quality of Bulk Titanium Materials Obtained by Powder Metallurgy Technology from Titanium Hydride Powder Used for Automotive Components

Titanium has excellent mechanical properties, low density, high chemical stability, good heat transfer properties and a good corrosion resistance. In recent years, a new process technology is emerging by which titanium and titanium alloys can be made by sintering titanium hydride (TiH2) and its mixture with alloying elements. The feasibility of this manufacturing approach has been fully demonstrated from powder to sintering and from microstructure to mechanical properties. This paper describes a study concerning Powder Metallurgy (PM) technology processing of Ti by conventional PM and non-conventional PM method such as Spark Plasma Sintering (SPS) route. The influence of the technological parameters on the micro-hardness and SEM microstructures during bulk titanium materials processing has been studied. The STATISTICA program has been used to monitor the influence of the technological parameters on the micro-hardness of bulk titanium processed products. The tribological behaviour of the bulk titanium materials on the basis of the coefficient of friction and wear rate is presented, too.

FRACTURE ANALYSIS OF POROUS P/M IRON BASED MATERIALS

Using powder metallurgy techniques new porous materials for self-lubricating bearings were developed. These materials are characterized by total porosity, which represents their major advantage for tribological applications, acting like their own oil reservoir. Sometimes the presence of pores can be also detrimental to the part performance. Among the causes of the bearings failure is their increased porosity for improving the lubricant retention capacity. Consequently, this can lead to a significant loss in strength. In the present work tensile test specimens based on Fe-Cu/brass-Sn-Pb powders were prepared in order to investigate the morphology of the fracture surfaces and to analyze the effect of pores on the failure process of these materials subjected to tensile loads. Distinct morphologies of the pores area were revealed by SEM images of the fracture surfaces.

Structural Analysis of PM Biocomposites Based on Hydroxyapatite Nanopowders Elaborated by Spark Plasma Sintering Route

The objective of this research is the development of a detailed structural analysis of biocomposites with ceramic matrix of hydroxyapatite (Hap) reinforced by titanium (Ti), elaborated by powder metallurgy technology. Nanometric Hap powders (<200nm) 75% wt and micrometric Ti powders (<150μm) are homogenized in a high energy ball mill Pulverisette 6. Spark plasma sintering (SPS) is the sintering route able to lead to nanostructured sintered samples when nanopowders are used as raw material. The SPS parameters are: the sintering temperature, T=(1000-1100)°C and the maintaining time, t=(10-20) minutes in vacuum. The influence of the sintering parameters on the composites structures is monitored using the optical microscopy (OM), electronic microscopy (SEM) and the X-Ray diffraction (XRD).