Densification of metals

Afaasjev, L. N., Roman, O. V., and Perelman, V. E., Eixperimental Determination of Parameters, Characterizing the Densification of Metal Powders, Conf. Perm, No. 

Ivensen, V. A. Densification of Metal Powders During Sintering Consultants Bureau New York, 1973. 

The densification of metal powders by HIP may sometimes involve filling the loose powder into a deformable metal container, but this method is unsuitable for most ceramic powders. Because of their fine size and low poured (or tap) density, considerable deformation and distortion of the material occurs during... 

The densification of metallic powders ( powder metallurgy ) involves HIP much more frequently than the densification of ceramic powders a search on the Web shows that most sites dealing with HIP relate to metallic products (the term taken in its largest sense and including cermets). 

When the powder is isostatically compacted at elevated temperatnres, the process is called hot isostatic pressing (HIP). In this case, the flexible dies are often made of thin metals, and high-pressnre gases snch as argon are nsed to heat the part rapidly and rednce thermal losses. Pressnre np to 100 MPa and temperatnres in excess of 2000°C are possible nsing HIP, and parts up to 600 kg can be fabricated. A schematic diagram of a typical HIP apparatus is shown in Figure 7.18. Metals that are processed commercially by HIP include various specialty steels, superalloys, hard metals, refractory alloys, and beryllium. We will see in Section 7.2 that HIP is also particularly useful for the densification of ceramic components. 

The thus obtained high-density Mn-Zn ferrite was investigated in detail from the view of physical and mechanical properties, that is, the relationships between the composition of metals (a,) ) and <5 the magnetic properties such as temperature and frequency dependence of initial permeability, magnetic hysteresis loss and disaccommodation and the mechanical properties such as modulus of elasticity, hardness, strength, and workability. Figures 3.13(a) and (b) show the optical micrographs of the samples prepared by the processes depicted in Fig. 3.12(a) and (b), respectively. The density of the sample shown in Fig. 3.13(a) reached up to 99.8 per cent of the theoretical value, whereas the sample shown in Fig. 3.13(b) which was prepared without a densification process, has many voids. 

A soft chemical route, known as the sol-gel method, has also been employed for the preparation of nano-oxides with uniform size and shape. This is a multistep process, usually consisting of hydrolysis of a metal alkoxide in an alcoholic solution to yield a metal hydroxide, followed by polymerization by elimination of water (gel-formation), drying off the solvent, and densification of the product to yield an ultrafine powder (Rao and Raveau, 1998 Khaleel and Richards, 2001). 

Another remarkable tendency results from the electrostatic repulsion of cations of small sizes. Transition metal-anion octahedra are linked by face sharing in the 2T phases of BaMnOs and CsNiFs, by comer sharing in the 3T (perovskite, see Section 4.3.2) phase of CsMnCb, and in a mixed way in BaRuOs (9L) and CsMnCb (9T). The sequential densification of 2L 9L 4T 6T 3T (perovskite)... 

Grebe, H. A., Advani, A., Thadani, N. N., and Kottke, T., Combustion synthesis and subsequent explosive densification of titanium carbide ceramics. Metall. Trans. A, 23A, 2365 (1992). 

Rabin, B. H., and Wright, R. N., Synthesis of iron aluminides from elemental powders reaction mechanisms and densification behavior. Metall. Trans. A, 22A, 277 (1991). 

Densification between two counter-rotating rolls. The (progressive) compacting of (metal) powders in rolling mills see also Powder rolling). 

Much of this knowledge is still phenomenological in character. A comprehensive theory of densification of particulate matter between counter-currently rotating rollers is not yet available, even though many similarities exist with the much better investigated and defined deformation of metals in rolling mills.2 ... 

TABLE 9.4 Effect of Metal Oxide Impurities on the Densification of MgO... 

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