Phase, intermetallic

Welding (qv) of titanium requires a protected atmosphere of iaert gas. Furthermore, parts and filler wire are cleaned with acetone (trichloroethylene is not recommended). The pieces to be welded are clamped, not tacked, unless tacks are shielded with iaert gas. A test sample should be welded. Coated electrodes are excluded and higher purity metal (lower oxygen content) is preferred as filler. Titanium caimot be fusion-welded to other metals because of formation of brittle intermetallic phases ia the weld 2oae. 

W. Pearson, P. Villars and L.D. Calvert, Pearson s Handbook of Crystallographic Data for Intermetallic Phases (American Society for Metals, Metals Park, Ohio, 1985). 

Fig. 1.58 Pit on aluminium showing how the rate of pitting may be facilitated by an intermetallic phase (Al3pe) or by a deposit of copper (after Wranglen )...

Another indication of the influence of precipitated phases on anodic behaviour may be seen in the curve for Alloy C in Fig. 4.28, where the small peak in the middle of the passive range is probably attributable to anodic dissolution of an intermetallic phase (n) and MjC carbide . ... 

Tin will protect copper from corrosion by neutral water. Pure tin is anodic to copper, and protects discontinuities by sacrificial corrosion. Both intermetallic phases are strongly cathodic to copper, and corrosion is stimulated at gaps in wholly alloyed coatings. An adequate thickness of tin is needed for long service, e.g. 25-50 xm. Another diffusion problem occurs with tin-plated brass. Zinc passes very quickly to the tin surface, where under conditions of damp storage zinc corrosion products produce a film... 

L361JH. H. Landoldt, R. Bomstein, Structure Data of the Elements and Intermetallic Phases, Vol. 

Values of A°(T) were obtained by using simulant elements which have the same number of bonding electrons as each intermetallic phase. Second law values of AH (298) were also obtained by use of heat capacities of the same simulant and constituent... 

The high reactivity of boron with many metals and the formation of brittle intermetallic phases. 

A laboratory preparation of pure Li uses a finely powdered mixture of Li,0 and a noble metal (Pt, Pd or Ir), which is heated > 1100°C in a stream of Hj. The pure intermetallic phase so produced is then heated under vacuum and the Li can be isolated by condensation from the vapor phase. ... 

The only effective way to identify and distinguish the intermetallic phases depicted in the phase diagrams (see 7.2.4.1.1) is by x-ray diffraetion, so their structures arc included here. 

In this group, the metals form compounds of the type Be M (M = Mg, Ca, Sr or Ba), MgjM (M = Ca, Sr or Ba) Mg4M or Mg23Mg (M = Sr or Ba) and MggM or Mg,7M2 (M = Sr or Ba) . These intermetallic phases are essentially identified and distinguished one from another by their x-ray diffraction patterns so their structures are included in this section. 

Two phase diagrams are available for lithium-copper systems. No intermetallic phases were found, but LiCu4 was later observed. Substantial solid solubility of lithium in copper approaching 20 at% at the melting point of Li has been observed. 

The phase diagram of the Li-Au system reveals a great deal of complexity, with separate intermetallic phases being formed based on thermal analysis supported by x-ray diffraction at specific compositions. Annealing, sometimes over long time periods, has been undertaken in some cases. 

The complete K-Hg phase diagram is compiled from three studies, and shows the formation of six intermetallic phases. A determination in the range 22-30 at% K indicates the formation of KHg2.7 . 

No phase diagram is available for the Cs-Zn or Cs-Cd systems. Tlie Cs-Hg system shows six intermetallic phases, but the accuracy of this determination is in doubt. ... 

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