Sintering characteristics of nanocrystalline TiO2—A study combining small angle neutron scattering and nitrogen absorption-BET

Small angle neutron scattering (SANS) was employed to characterize the pore structure of nanophase TiO2 ceramic materials compacted at different temperatures. Nanophase samples, produced by inert gas condensation, were compacted at 25, 290, 413, and 550 °C using a pressure of 1 GPa. The pore size distribution of the sample compacted at room temperature was very broad, with sizes ranging from 3-30 nm and pores comprising 38% of the sample volume. Compaction at 290 and 413 °C reduced the pore volume to 25% and 20%, respectively, by eliminating pores at both the small and large ends of the distribution. Compaction at 550 °C resulted in a pore volume that was less than 8%. Complications in the SANS analysis arising from the scattering from grain boundaries are discussed. The results from SANS are compared with those derived from nitrogen absorption, BET, measurement

Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe7Pd3ferromagnetic shape memory alloy thin films

Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the face-centered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ion-irradiation-induced austenite $\Rightarrow$ martensite and inter-martensite transitions, explore the multi-variant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiation-induced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite ⇔ martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys

Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe₇Pd₃ ferromagnetic shape memory alloy thin films

Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the facecentered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ionirradiation-induced austenite⇒martensite and inter-martensite transitions, explore the multivariant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiationinduced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite⇔martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys

Ion-irradiation studies of cascade damage in metals

Ion-irradiation studies of the fundamental aspects of cascade damage in metals are reviewed. The emphasis of these studies has been the determination of the primary state of damage (i.e. the arrangement of atoms in the cascade region prior to thermal migration of defects). Progress has been made towards understanding the damage function (i.e. the number of Frenkel pairs produced as a function of primary recoil atom energy), the spatial configuration of vacancies and interstitials in the cascade and the cascade-induced mixing of atoms. It is concluded for these studies that the agitation of the lattice in the vicinity of energetic displacement cascades stimulates the defect motion and that such thermal spike motion induces recombination and clustering of Frenkel defects. 9 figures

Influences of thermal spikes in ion beam mixing

Guided by the results of molecular dynamics simulations, we develop a thermal spike model for the relaxation of collision cascades in which the hot zone has mobile, reacting defects and cools by thermal diffusion. Marker atoms within such spikes are taken to migrate by radiation enhanced diffusion which is governed by the locally transient temperatures and defect concentrations. The atomic mixing associated with such motions is examined, on the basis of the model, for a variety of ion-target systems. The dependences of spike mixing on diffusion mechanism, irradiation ion and energy, and sample temperature are discussed. 11 references, 4 figures, 1 table

Reactive epitaxy of Co nanoparticles on (111)Si

10.1093/jmicro/50.6.545Journal of Electron Microscopy506545-548JELJ

Ball milling of systems with positive heat of mixing

Ball milling of systems with positive heat of mixing : effect of temperature in Ag-Cu / T. Klassen ; U. Herr ; R. S. Averback. - In: Acta materialia. 45. 1997. S. 2921-293

Characterization of near surface regions in irradiated Ni(Si) alloys

Transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), Auger electron spectroscopy (AES), and infra-red pyrometry (IRP) have been used to characterize the growth of Ni/sub 3/Si films on the surfaces of irradiated Ni(Si) alloys. Results from each of the four techniques are presented and discussed, and comparisons are made between the different techniques. AES measurements are reported which suggest that Si concentrations significantly in excess of that found for stoichiometric Ni/sub 3/Si are induced in regions very near to the surface during irradiation