Powder Sintering from Blended Elemental (BE) Powder Mixture

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Powder mixing

Powder mixing is a process by which two or more different component powders are uniformly mixed. Mixing quality would not only affect the shaping process and the quality of the compacts, but also seriously affect the sintering process and the quality of final products. There are two methods of mixing: mechanical mixing and chemical mixing; the mechanical mixing is the most common technique and there is introduced here.
Commonly used machines for mechanical mixing are ball mill mixer, V-blender, conical mixer and spiral mixer, etc. Mechanical mixing includes dry mixing and wet mixing. Dry mixing is commonly used in producing iron-based products. Carbide alloy mixtures are normally prepared by wet mixing method. The commonly used liquid media for wet mixing are ethanol, gasoline and acetone, etc. In order to ensure that the wet mixing process can be carried out successfully, wet mixing media (1) do not chemically react with the material, (2) should not have a low boiling point or be volatile, (3) should be non-toxic, (4) should be resourceful and with low cost.
In some cases, the powder particle size is too big and hence causes compaction and sintering problems. Large particles need a higher compaction pressure and usually result in a low green density, which further leads to a low sintered density in the final product.
Therefore, reduction in particle size is required. One technique for reducing particle size is mechanical milling (MMing). In addition to the particle size reduction, MMing can also lead to the formation of a fine microstructure. In the two-component powders, it is often to form a fine-grained composite microstructure. Such fine composite microstructure promotes the densification process during sintering, as the diffusion pathway between the particles is reduced.

Mechanical milling (MMing) and alloying (MAing)

MMing or MAing is a powder preparation technique which has been developed in the last two decades. In MMing or MAing process, a suitable powder charge (typically, a blend of elemental powders) with a suitable milling medium is placed in a high energy mill.
Vigorous shock and collision from milling media (balls) to powder particles, repeating deformation, breakage and welding together between the powders happen. In some cases, mutual diffusion and solid-state reaction happen. A schematic diagram of MMing is shown in Fig. 2.12. MAing is only named, if alloy or compound powder forms when the milling time is sufficiently long.
The objectives of MMing are to reduce the particle size and change particle shape, to mix and blend and to synthetize nanocomposite. The typical high energy mill instruments include tumbler ball mills, vibratory mills, planetary mills, and attritor mills, [96]. The kinetics of MMing depends on the energy transferred to the powder from the balls during milling [97]. Many parameters would affect the energy transfer, including mill types, milling speed, ball size and size distribution, dry or wet milling, milling temperature and milling time.

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Chapter 1 Introduction
1.1 Background
1.2 Objectives
1.3 Thesis outline.
Chapter 2 Literature Review
2.1 Biomaterials.
2.2 Biodegradable materials
2.2.1 Biodegradable polymers
2.2.2 Biodegradable metals
2.2.3 Biodegradable Mg and Mg alloys
2.3 Biodegradable iron and its alloy
2.3.1 Pure iron
2.3.2 Alloy development by incorporating Mn .
2.3.3 Mn in human body
2.4 Fe-Mn alloys as biodegradable materials
2.5 Production of Fe-35wt.%Mn alloys by powder metallurgy
2.5.1 Powder mixing
2.5.2 Powder compaction
2.5.3 Sintering
2.6 Potential biomedical applications of Fe-35wt.%Mn alloys
2.6.1 Coronary artery stenting
2.6.2 Orthopaedics
Chapter 3 Experimental
3.1 Sample preparation
3.1.1 Powder preparation
3.1.2 Die compaction .
3.1.3 Debinding
3.1.4 Sintering
3.2 Measurement of density, porosity and open porosity
3.3 Characterization of microstructures.
3.4 Corrosion evaluation.
3.5 Mechanical properties
3.6 Cell compatibility
Chapter 4 Powder Sintering from Blended Elemental (BE) Powder Mixture
4.1 Introduction
4.2 Processing.
4.3 Results and discussion
4.4 Summary.
Chapter 5 Powder Sintering from Mechanically Milled (MMed) Powder.
Chapter 6 Porous Fe-35wt.%Mn Produced via Sintering from NH4HCO3 Porogen
Chapter 7 Stress Corrosion Cracking (SCC) of Fe-35wt.%Mn Alloys .
Chapter 8 Cytocompatibility of Fe-35wt.%Mn Alloys
Chapter 9 Conclusions and Future Work
References