Papers by Keyword: Solute Diffusion

Abstract: In this Chapter, we review knowledge about diffusion in quasi-crystalline alloys (quasicrystals). In Section 1 we first remind the reader of some major aspects of the quasi-crystalline state and in Section 2 we introduce phase diagrams with quasi-crystalline phases, for which detailed diffusion studies are available. We mention in Section 3 the more common experimental methods for diffusion studies. The diffusive motion of atoms in quasi-crystalline alloys can be studied by the same techniques used for crystalline metallic alloys and intermetallics – measurements of radiotracer diffusion and diffusion of stable isotopes and solute atoms by SIMS profiling. The best-studied quasi-crystalline alloys are icosahedral AlPdMn, icosahedral ZnMgRE (RE = rare earth metal), and decagonal AlNiCo. The major diffusion results for these quasicrystals are reviewed in Sections 4, 5, and 6. Section 7 is devoted to the pressure dependence of diffusion in quasicrystals and to a comparison of the activation volumes with those of crystalline metals. Positron annihilation studies are also mentioned, which together with activation volumes for diffusion strongly favour a vacancy mechanism in quasicrystals. The major results and conclusions are summarized in Section 8.

Abstract: 800x600 Intermetallics are compounds of two metals or of metal(s) and semimetal(s). Their structures are usually different from those of the constituents. Some intermetallics are interesting functional materials, others have attracted attention as high-temperature structural materials. We remind the reader of some fundamentals of solid-state diffusion and to the major techniques for tracer diffusion measurements, interdiffusion studies and the growth kinetics of layers in solid diffusion couples. Starting from self-diffusion, which is the most basic diffusion phenomenon in any solid, the paper covers the main features of diffusion in binary intermetallics from the systems Cu-Zn, Ni-Al, Fe-Al, Mg-Al, Ni-Ge, Ni-Ga, Fe-Si, Ti-Al, Ni-Mn, Mo-Si, Co-Nb and Ni-Nb.. We illustrate the influence of phase transitions on diffusion and point out some common features of diffusion in intermetallics. We discuss in detail diffusion in silicides of iron, molybdenum and of silicides of refractory metals. We also consider aluminides of iron, nickel, and titanium and in the aluminium-magnesium system. We consider diffusion in intermetallics of the cobalt-niobium and nickel-niobium system and in in the Nb-Sn and V-Ga systems. We finish with some remarks about grain boundary diffusion in intermetallics. Normal 0 21 false false false UK X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif";}

Abstract: Starting from fundamental aspects of thermal vacancies and solid-state self-and solute diffusion, this paper reviews procedures for tracer-and interdiffusion studies and of the major techniques for vacancy studies by dilatometry and positron annihilation in metals. Equilibrium vacancy and diffusion studies performed on pure iron and aluminium are mentioned at first. We also comment some peculiarities of solute diffusion in aluminium. Positron annihilation and differential dilatometry studies for Fe-Al alloys with various compositions are summarized and new experimental studies by the authors are reported for vacancy migration in Fe₆₁Al₃₉. All these studies indicate a relatively high fraction of thermal vacancies with relatively low mobility in this type of iron-aluminides as compared to pure metals. Tracer diffusion of iron and of several substitutional solutes such as Co, Ni, Cr, Mn, Zn, and In in Fe-Al from the Münster laboratory are summarized. The diffusion studies of Fe-Al cover various alloy composition between Fe₃Al and FeAl and several structures such as A2, B2 and D0₃. Interdiffusion coefficients obtained from diffusion couples between Fe-Al alloys are discussed together with Fe tracer diffusion data. The Darken-Manning equation is used to deduce Al diffusivities therefrom. The latter are hardly accessible to radiotracer experiments due to a lack of a suitable Al tracer. Diffusion of Al is slightly faster than diffusion of Fe indicating diffusion mechanisms with coupled jumps of Fe and Al atoms.

Abstract: Starting from some fundamentals of solid-state diffusion, we remind the reader to the major techniques for lattice diffusion measurements. Self-diffusion is the most basic diffusion phenomenon in any solid. The paper covers main features of self-diffusion in pure fcc and bcc metals and some important facts about diffusion of substitutional solutes in metals. Binary intermetallics are compounds of two metals or of a metal and a semimetal. Their structures are different from those of the constituents. Some intermetallics are interesting functional materials others have attracted attention as high-temperature structural materials. The paper reviews some results mainly from our laboratory on diffusion in binary intermetallics from the systems Cu-Zn, Ni-Al, Fe-Al, Ni-Ge, Ni-Ga, Fe-Si, Ti-Al, Ni-Mn, Mo-Si and Co-Nb, which have been published in detail elsewhere. Some results for the ternary system Ni-Fe-Al are also mentioned.

Abstract: The results on modeling dendritic solidification from undercooled melts processed by the electromagnetic levitation technique are discussed. In order to model the details of formation of dendritic patterns we use a phase-field model of dendritic growth in a pure undercooled system with convection of the liquid phase. The predictions of the phase-field model are discussed referring to our latest high accuracy measurements of dendrite growth velocities in nickel samples. Special emphasis is given to the growth of dendrites at small and moderate undercoolings. At small undercoolings, the theoretical predictions deviate systematically from experimental data for solidification of nickel dendrites. It is shown that small amounts of impurities and forced convective flow can lead to an enhancement of the velocity of dendritic solidification at small undercoolings.