Anelastic Phenomena Preceding the Melting of Pure Metals and Alloys

2016 ◽  
Vol 879 ◽  
pp. 66-71 ◽  
Author(s):  
Roberto Montanari ◽  
Alessandra Varone
Keyword(s):  
Energy Loss ◽  
Dynamic Modulus ◽  
Flexural Vibration ◽  
Mechanical Spectroscopy ◽  
Sharp Drop ◽  
Temperature Range ◽  
Interstitial Concentration ◽  
Theory Of Melting ◽  
Pure Metals ◽  
Specific Metal

Precursor phenomena of melting in pure metals (In, Pb, Bi and Sn) and alloys of the systems Pb-Bi and In-Sn with different compositions have been investigated by means of Mechanical Spectroscopy (MS), i.e. dynamic modulus and damping measurements. MS tests evidenced that a sharp drop of dynamic modulus E takes place in a temperature range ΔT before the formation of the first liquid: the modulus variation ΔE and the corresponding temperature range ΔT depend on the specific metal or alloy. The modulus drop is consistent with a relevant increase of interstitial concentration (self-interstitials assuming the dumbbell configuration), as predicted by the Granato’s theory of melting. The increase of damping in the same temperature range of modulus drop supports this explanation. Owing to their dumbbell configuration self-interstitials interact with the flexural vibration of samples and the periodic re-orientation under the external applied stress leads to energy loss and damping increase. The increase of self-interstitials has the effect to weaken interatomic bonds (modulus drop) and favours the collapse of crystal lattice (melting).

Physical Phenomena Leading to Melting of Metals

2017 ◽  
Vol 884 ◽  
pp. 3-17 ◽  
Author(s):  
Roberto Montanari ◽  
Alessandra Varone
Keyword(s):  
Dynamic Modulus ◽  
X Ray Diffraction ◽  
Mechanical Spectroscopy ◽  
Sharp Drop ◽  
X Ray ◽  
Novel Method ◽  
Diffraction Peaks ◽  
Pure Metals ◽  
Physical Phenomena ◽  
Specific Metal

Precursor phenomena of melting in pure metals and alloys have been investigated by means of Mechanical Spectroscopy (MS) and High Temperature X-ray Diffraction (HT-XRD). The examined materials were the pure metals In, Sn, Pb and Bi, and some alloys of the systems In-Sn and Pb-Bi with different compositions.MS tests have been carried out by means of a novel method developed by us that permits to operate in resonance conditions and employs hollow reeds of stainless steel containing the liquid metal. In all the metals a sharp drop of dynamic modulus and a Q-1 maximum were observed in a temperature range ΔT before melting that depends on the specific metal and its structure. Such anelastic behaviour is consistent with an increase of the interstitialcies concentration as predicted by the Granato’s theory.Moreover, HT-XRD evidenced that sudden grain re-orientation, shift and broadening of diffraction peaks occur just before the formation of the first liquid, therefore self-interstitials and vacancies seem to play a synergic role in melting. The increase of self-interstitials over ΔT has the effect of weakening interatomic bonds that favours the successive vacancy avalanche leading to the collapse of crystal lattice (melting).

scholarly journals Межфазные напряжения и аномальный вид кривых псевдоупругой деформации в кристаллах сплава Ni-=SUB=-49-=/SUB=-Fe-=SUB=-18-=/SUB=-Ga-=SUB=-27-=/SUB=-Co-=SUB=-6-=/SUB=-, деформированных сжатием в направлении оси [011]-=SUB=-A-=/SUB=-

2019 ◽  
Vol 89 (6) ◽  
pp. 873
Author(s):  
Г.А. Малыгин ◽  
В.И. Николаев ◽  
В.М. Крымов ◽  
С.А. Пульнев ◽  
С.И. Степанов
Keyword(s):  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Elastic Moduli ◽  
Sharp Decrease ◽  
Transformation Kinetics ◽  
Sharp Drop ◽  
Interfacial Stresses ◽  
Temperature Range ◽  
Deformation Curves

AbstractWe have performed experimental and theoretical investigation of the anomalous form of the compression diagrams and shape memory restoration curves in Ni_49Fe_18Ga_27Co_6 alloy crystals deformed by uniaxial compression along the [011]_ A crystallographic direction ( A -austenite) in the temperature range of 200–350 K. It is found that in the investigated temperature range, all compression diagrams contain anomalous segments of smooth and sharp decrease in deforming stresses. It is shown that the segments of a smooth decrease in stress are associated with peculiarities in martensite reaction L1_2 → 14M, while segments of a sharp drop are due to instability of martensite reactions 14M → L1_0 and L1_2 → L1_0. A possible source of reaction instability is associated with interfacial stresses at the interfaces between the martensite and austenite phases (lamellas) due to different elastic moduli of contacting phases. The magnitude of these stresses is significant in the case of 14M → L1_0 and L1_2 → L1_0 transformations, which induces a sharp drop of the deforming stress, while the restoration of the shape memory effect is of a burst nature. It is established that the contribution of interfacial stresses to the free energy of martensite transformation is smaller than the dissipative (entropy) contribution to this energy; however, interfacial stresses higher than a certain threshold strongly affect transformation kinetics and, hence, determine the strongly anomalous shape of pseudoelastic deformation curves and burst restoration of the shape memory effect.

TRANSPORT PROPERTIES OF PURE METALS AT HIGH TEMPERATURES: I. COPPER

1967 ◽  
Vol 45 (11) ◽  
pp. 3677-3696 ◽  
Author(s):  
M. J. Laubitz
Keyword(s):  
High Temperature ◽  
Transport Properties ◽  
High Temperatures ◽  
Pure Copper ◽  
High Temperature Properties ◽  
Temperature Range ◽  
Pure Metals

This paper is the first of a series reporting our investigations into the high-temperature properties of the monovalent metals. It contains a description of the methods used in these investigations, and the results of measurements of the transport properties of pure copper, over the temperature range 300–1 250 °K. These results are compared with some previously published work, and also with standard theoretical expressions applicable to the monovalent metals.

Study on Cu48Zr43Al9 and Cu54Zr40Al6 Amorphous Matrix Alloys by Mechanical Spectroscopy

2015 ◽  
Vol 365 ◽  
pp. 317-322
Author(s):  
Odila Florêncio ◽  
Paulo Wilmar Barbosa Marques ◽  
Paulo Sergio Silva ◽  
Javier Andres Muñoz Chaves ◽  
L.C. Rodriguez Aliaga ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Internal Friction ◽  
Amorphous Matrix ◽  
Glassy State ◽  
Flexural Vibration ◽  
Amorphous Structure ◽  
Mechanical Relaxation ◽  
Nominal Composition ◽  
Mechanical Spectroscopy ◽  
Casting Technique

Anelastic properties of Bulk Metallic Glasses (BMG) were studied by mechanical spectroscopy using a flexural vibration apparatus. BMG’s samples, with nominal composition Cu48Zr43Al9and Cu54Zr40Al6, were produced by skull push-pull casting technique in rectangular cavity cooper mold. In both samples, the differential scanning calorimeter patterns have evidenced the presence of amorphous structure, although the X-ray diffraction for Cu48Zr43Al9composition has shown a heterogeneous microstructure embedded in the amorphous matrix. Anelastic relaxation spectra were obtained using an acoustic elastometer system with vibration frequency in the kilohertz bandwidth, a heating rate of 1 K/min, vacuum greater than 10-5mBar in the temperature range of 300 K to 620 K. In the flexural apparatus, an acoustic elastometer system, the internal friction (energy loss) and the elastic modulus were obtained by free decay of vibrations and by the squared of the oscilation frequency, respectively. Internal friction spectra were not reproducible among the measurements, which may imply atomic rearrangement in the samples due to consecutive heating. Normalized elastic modulus data showed distinct behavior from the first to the other measurements evidencing irreversible microstructural alterations in the samples possibly associated with mechanical relaxation due to the motion of atoms or clusters in the glassy state.

Structural Changes of Liquid Pb-Bi Eutectic Alloy

2012 ◽  
Vol 706-709 ◽  
pp. 878-883 ◽  
Author(s):  
Paolo Deodati ◽  
Franco Gauzzi ◽  
Roberto Montanari ◽  
Alessandra Varone
Keyword(s):  
Dynamic Modulus ◽  
Structural Changes ◽  
Distribution Functions ◽  
X Ray Diffraction ◽  
Mechanical Spectroscopy ◽  
Neutron Spallation Source ◽  
Driven System ◽  
Spallation Source ◽  
Accelerator Driven System ◽  
Diffraction Patterns

Liquid Pb–Bi eutectic (LBE) alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system (ADS). The alloy has been characterized in liquid state from melting (125 °C) to 750 °C by mechanical spectroscopy, i.e. internal friction (IF) and dynamic modulus measurements. The experiments have been carried out using hollow reeds of austenitic stainless steel filled with Pb-Bi alloy and sealed at the extremities. Dynamic modulus showed a remarkable drop in the range 350-520 °C. In the same temperature range radial distribution functions (RDFs), determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The phenomenon has been explained as a structural re-arrangement of atoms in the liquid metal.

Ethylene on cleaved silicon: High-resolution electron-energy-loss study of an unusual adsorption system in the temperature range 85–300 K

1987 ◽  
Vol 35 (3) ◽  
pp. 1461-1464 ◽  
Author(s):  
M. N. Piancastelli ◽  
M. K. Kelly ◽  
D. G. Kilday ◽  
G. Margaritondo ◽  
D. J. Frankel ◽  
...  
Keyword(s):  
High Resolution ◽  
Energy Loss ◽  
Electron Energy ◽  
Adsorption System ◽  
Temperature Range ◽  
Resolution Electron ◽  
Electron Energy Loss

scholarly journals Electron Energy-loss Spectra of the Alloys Al?Mg, Cd?Mg, and Cu?Ni

1970 ◽  
Vol 23 (5) ◽  
pp. 655 ◽  
Author(s):  
BM Hartley ◽  
JB Swan
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Band Structures ◽  
Pure Metals ◽  
Electron Energy Loss ◽  
Electron Energy Loss Spectra

Characteristic electron energy-loss spectra of the alloys AI-Mg, Cd-Mg, and Cu-Ni are presented. These spectra are interpreted in terms of expected changes in the band structures of the pure metals on alloying.

Sign in / Sign up

Export Citation Format

Share Document