Martensitic Transformation Parameters Research Articles

The influence of the chemical composition of the Ti-Hf-Zr-Ni-Cu-Co shape memory alloys on the structure and the martensitic transformations

Twelve senary alloys were manufactured with different concentrations of doping elements (Hf, Zr, Ni, and Cu) that varied from 1 to 17 at%, and the concentration of the Ni equivalent (Ni, Cu, and Co) atoms changed from 49 to 51 at%. It allowed the production of Ti-Hf-Zr-Ni-Cu-Co alloys with various configuration entropies. It was found that, regardless of the entropy value, all alloys crystallised in the B2 phase, in which the lattice parameter increased upon a rise in the doping elements’ concentration (X parameter) and was hardly affected by the Ni group concentration ([Ni] = Ni + Cu + Co). In the alloys with low and medium entropy, the chemical composition of the B2 phase was homogeneous and close to the composition of the alloy. In the alloys with high entropy, the core and edge of dendrite cells in the matrix were characterised by different concentrations of doping elements, while the concentration of the Ni group was constant. Besides the B2 phase, the secondary phase existed in all alloys, whose type [Ti]2[Ni] or [Ni]4[Ti]3 depended on the [Ni] value, as was observed in the binary NiTi alloys. It was found that the Ti-Hf-Zr-Ni-Cu-Co alloys with low and medium entropy underwent the B2 ↔ B19′ martensitic transformation on cooling and heating. An increase in the [Ni] and X values initiated the formation of the strain nanodomains on cooling before the forward transformation. In the high-entropy alloys with X = 10 at%, the strain nanodomains formed on cooling to − 180 °C without the formation of the B19′ phase. In the alloys with X = 17 at%, strain nanodomains, and martensitic transformation were not found on cooling, but the martensitic transformation was initiated by loading at − 100 °C. It was shown that the variation in the Ni group concentration affected the martensitic transformation parameters only in the low-entropy alloys. In the medium- and high-entropy alloys, the concentration of the doping element had a more significant effect on the transformation than the [Ni] value.

Impact of Pre-formed Martensite on the Electromagnetic Properties and Martensitic Transformation Kinetics of Uniaxially Tensile Loaded 304 Stainless Steel

The investigation addresses the influence of tensile deformation on the magnetic properties of 304SS samples in their as-received state as well as those with martensite content of 12 and 17%. Non-destructive electromagnetic techniques like magnetic Barkhausen emission (MBE) and magnetic hysteresis loop have been used to measure variation in MBE voltage and coercivity, respectively, during plastic deformation through tensile loading. As both the techniques use surface probe, the present investigation will be useful for in situ evaluation of structural components. With progressive plastic deformation, those measurements revealed different stages of deformation indicated by change in MBE signal and magnetic coercivity. The stages of magnetoelastic response, strain-induced martensitic transformation, dislocation pile-ups and formation of voids reflected different patterns of magnetic Barkhausen emission and magnetic coercivity variation with progressive straining of austenitic stainless steel samples. The changes in true strain with variation in martensite content along gauge length of fractured samples have been analyzed with respect to martensite transformation kinetics. Mathematical fitting methodology has been adopted to distinguish as-received and pre-strained martensitic transformation characteristics. In situ magnetic NDE and associated martensitic transformation parameters may be useful for structural health monitoring of in-service components.

Variations in martensitic transformation parameters due to grains evolution during post-deformation heating of Ti-50.2 at.% Ni alloy amorphized by HPT

The structure and martensitic transformations in Ti-50.2at.% Ni alloy subjected to high-pressure torsion (HPT) and post-deformation heating were studied. It was shown that HPT under 8GPa for 3.5 turns resulted in an amorphization of the alloy structure but the crystalline debris remained. Further heating of the sample led to alloy crystallization and the bimodal grain size structure formed. The first group of grains underwent a B2↔R transition when the average grain size was varied from 20 to 50nm, and a B2→R→B19′I transformations when the average grain size was 80nm or more. The second group of grains underwent a B2↔B19′II transformation. An increase in temperature of amorphous sample heating led to a rise in grain size and as a result, the temperatures of the martensitic transformations changed. The temperatures of the B19′I→B2 transformation and the B2↔R transition increased when the heating temperature changed from 359 to 550°C whereas, the temperatures of the B2↔B19′II transformation increased if the amorphous sample was subjected to heating from 415 to 550°C when the recrystallisation took place. It was assumed that the bimodal grain distribution was caused by the grain appeared during crystallization in two ways: from the amorphous phase and from the debris remained in the amorphous phase after HPT.

Atomic Ordering and Parameters of Martensitic Transformation in Fe-based Alloys

Evolution of martensitic transformation (MT) start temperatures, hysteresis and shape recovery in Fe-Ni, Fe-Ni-Sm and Fe-Pt alloys with ordering has been studied. Atomic ordering and position disordering (alloying) are determined as factors of control over mentioned parameters. It is found out that samarium alloying increases MT start temperatures and improves shape recovery. Quenching from 800-900° C into room temperature water is the most appropriate solution treatment to acquire extreme parameters of martensitic transformation: minimum in MT temperature hysteresis and shape recovery.

Effect of thermal cycling on martensitic γ↔ε-transformation in alloy Fe – 22% Mn – 3% Si

Methods of mechanical spectroscopy and differential scanning calorimetry demonstrate the effect of thermal cycling for a specimen of alloy Fe – 22% Mn – 3% Si through the martensitic transformation range on martensitic transformation parameters: points for the start and end of transformation, amount of thermal hysteresis, and transformation development kinetics.

Study of martensitic transformation in the Fe-22 Mn-3 Si alloy by mechanical spectroscopy

Methods of mechanical spectroscopy (determination of the internal-energy dissipation and the elasticity modulus), X-Ray diffraction, and calorimetry have been used to study the specific features of the reversible martensitic transformation in the Fe—22Mn—3Si alloy (wt %). A detailed study has been given to the specific features of the internal-energy dissipatio n during the direct and reverse martensitic transformations in a wide range of heating rates, frequencies, and deformation amplitudes. Particular emphasis has been placed on multiple thermal cycling of the sample through the martensitic-transformation range and its effect on the martensitic-transformation parameters, such as the transformation start and finish temperatures, the value of the thermal hysteresis, and the transformation kinetics.

Effect of scandium and yttrium on martensitic transformations in TiNi-based alloys

The paper examines the effect of scandium and yttrium additions (up to 5 and 10 at.%, respectively) on martensitic transformations and shape memory effect in TiNi. The martensitic temperature decreases differently in quenched TiNi-ScNi and TiNi-YNi alloys. The martensitic temperature dependence on scandium concentration is linear, and doping TiNi alloy with yttrium smoothly decreases the temperature to about 30°C at 10 at.% yttrium. The martensitic transformations in both systems are accompanied by the 100% shape memory effect. When titanium is replaced by a small amount of scandium (0.01 at.%.), the nature and parameters of martensitic transformation remain unchanged.

Quantification of ∊-martensite after thermocycling in Fe-(17∼25)Mn alloys

Abstract Fe-(17∼25)Mn alloys have been systematically investigated by means of X-ray diffraction, optical microscopy, differential scanning calorimetry and dilatometry. Such parameters of martensitic transformation as transformation temperatures, enthalpy, phase composition and microstructural changes are discussed taking into account the effect of thermocycling. A special focus is laid on the incompleteness of the γ → ∊ transformation that is attributed mainly to the antiferromagnetic → paramagnetic transition of austenite. The volume fraction of epsilon martensite has been determined using the results from X-ray diffraction and dilatometry tests.

Influence of the Ga Alloying on the Properties of NiAl Based Alloys

Influence of the Ga alloying on the crystal structure and parameters of the martensitic transformation are presented. X-ray diffraction has shown the multiphase composition of the samples (β (B2)- phase, γ′ (L12)-phase, (L10)-martensitic phase, Ni5Al3-phase). Metallographic investigations have demonstrated the coarse grain of B2 phase with non-regular needles of Ni3Al and typical martensitic structure. Ga did not suppress the martensitic transformation in NiAlGa alloys. The Ni to Al ratio and quantity of Ga determine the parameters of martensitic transformation.

B2 Intermetallic Compounds of Zr. New Class of the Shape Memory Alloys

It is known that the B2 equiatomic intermetallic compounds of Zr (ZrCo-based [1], ZrCu [2], ZrRh [3]) undergo a martensitic transformation (MT) with wide temperature hysteresis. It was found that the MT is accompanied by the perfect shape memory effect (SME) for ZrCu [2] and ZrRh [3]. In this report we represent the results of structural analysis, electrical resistivity, calorimetric and SME measurements for ZrCu- and ZrCo-based compounds. Interrelation between structural, thermodynamical parameters of MT and SME in this alloys will be described. The shape memory aspects of this potential alloys for the application at high temperatures will be discussed.

Improvement of the shape-memory effect properties of copper alloys by optimization of the heat-treatment regimen

Review of engineering methods for the heat treatment of copper alloys with a thermoelastic martensitic transformation, particularly alloys belonging to the Cu-Al-Zn, Cu-Al-Mn, and Cu-Al-Ni systems. The effectiveness of utilizing a multifactor experiment based on the mathematical theory of experimental design in order to determine the optimum heat-treatment regimen for copper alloys possessing the shape-memory effect (SME) with neighboring martensitic transformation parameters is shown. The basic structural and phase changes produced by heat treatment which lead to a strengthening of the SME are elucidated. 20 refs., 1 fig., 3 tabs.