Gabriela Sima

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.

Fracture Behavior as Selection Criterion for Alloplastic Bone Graft Applications

Designing and processing of the alloplastic bone grafts represent one of the newest trends in bone tissue engineering, solving a lot of trauma problems of the patients simultaneously with technological and economical achievements. Recent developments in the field provide advantageous aspects concerning the internal architecture, mechanical properties and biocompatibility of the alloplastic bone grafts processed by the powder metallurgy (PM) technology. In this respect, the PM biocomposite materials based on hydroxyapatite powder particles reinforced by metallic or ceramic powders afford great benefits combining classic PM processes with different foaming techniques. The obtained biocomposites present special morphological and structural features matching the genuine bone tissue to be grafted, cortical respectively trabecular. This study focuses on the mechanical testing of the hydroxyapatite-based biocomposites reinforced by different foaming agents, specifically TiH2, CaCO3 and NH4HCO3 up to 25% mass. The overlapping of the obtained experimental results with those reported by the literature leads to the conclusion that the mechanical response of the PM biocomposites studied in this paper may play as a selection criteria to depict their application in hard tissue engineering.

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).