Possibility of valence-fluctuation mediated superconductivity in Cd-doped CeIrIn5_5 probed by In-NQR

We report on a pressure-induced evolution of exotic superconductivity and spin correlations in CeIr(In$_{1-x}$Cd$_{x}$)$_5$ by means of In-Nuclear-Quadrupole-Resonance (NQR) studies. Measurements of an NQR spectrum and nuclear-spin-lattice-relaxation rate $1/T_1$ have revealed that antiferromagnetism induced by the Cd-doping emerges locally around Cd dopants, but superconductivity is suddenly induced at $T_c$ = 0.7 and 0.9 K at 2.34 and 2.75 GPa, respectively. The unique superconducting characteristics with a large fraction of the residual density of state at the Fermi level that increases with $T_c$ differ from those for anisotropic superconductivity mediated by antiferromagnetic correlations. By incorporating the pressure dependence of the NQR frequency pointing to the valence change of Ce, we suggest that unconventional superconductivity in the CeIr(In$_{1-x}$Cd$_{x}$)$_5$ system may be mediated by valence fluctuations.Comment: Accepted for publication in Physical Review Letter

Low cost estimation of Wöhler and Goodman–Haigh curves of Ti-6Al-4V samples by considering the stress ratio effect

The stress ratio effect on the fatigue life of materials is a topic which have been studied by two different approaches. On the one hand, several experiments, performed under different stress ratios are necessary to estimate the corresponding Wöhler curves. Afterwards, these curves are considered to estimate the fatigue life under a particular stress range. On the other hand, fatigue failure criteria for fluctuating stress like the Goodman–Haigh relationship, are applied to estimate the stress amplitude for a constant fatigue life. Based on the Stüssi function, this paper presents a low cost model to estimate Wöhler curves and constant fatigue Goodman–Haigh diagrams. This procedure requires a set of tests performed under a particular stress ratio from LCF to HCF, and data from minimum two additional stress ranges for each subsequent stress ratio. An application on data from Ti-6Al-4V samples manufactured by selective laser melting (SLM) is presented

A fabrication guide for planar silicon quantum dot heterostructures

We describe important considerations to create top-down fabricated planar quantum dots in silicon, often not discussed in detail in literature. The subtle interplay between intrinsic material properties, interfaces and fabrication processes plays a crucial role in the formation of electrostatically defined quantum dots. Processes such as oxidation, physical vapor deposition and atomic-layer deposition must be tailored in order to prevent unwanted side effects such as defects, disorder and dewetting. In two directly related manuscripts written in parallel we use techniques described in this work to create depletion-mode quantum dots in intrinsic silicon, and low-disorder silicon quantum dots defined with palladium gates. While we discuss three different planar gate structures, the general principles also apply to 0D and 1D systems, such as self-assembled islands and nanowires.Comment: Accepted for publication in Nanotechnology. 31 pages, 12 figure

Fatigue crack paths and properties in A356-T6 aluminum alloy microstructurally modified by friction stir processing under different conditions

A356-T6 cast aluminum alloy is a light weight structural material, but fatigue crack initiates and propagates from a casting defect leading to final fracture. Thus it is important to eliminate casting defects. In this study, friction stir processing (FSP) was applied to A356-T6, in which rotating tool with probe and shoulder was plunged into the material and travels along the longitudinal direction to induce severe plastic deformation,resulting in the modification of microstructure. Two different processing conditions with low and high toolrotational speeds were tried and subsequently fully reversed fatigue tests were performed to investigate theeffect of processing conditions on the crack initiation and propagation behavior. The fatigue strengths weresuccessfully improved by both conditions due to the elimination of casting defects. But the lower tool rotationalspeed could further improve fatigue strength than the higher speed. EBSD analyses revealed that the higher tool rotational speed resulted in the severer texture having detrimental effects on fatigue crack initiation andpropagation resistances.&nbsp

EBSD-assisted fractographic analysis of crack paths in magnesium alloy

 Magnesium (Mg) alloys are attractive as structural materials due to their light weight and high specific strength. It is well known that Mg alloy has hexagonal close-packed (HCP) structure and only basal slipor twinning can operate during plastic deformation because critical resolved shear stresses of the other slipsystems such as pyramidal or prismatic slips are much higher than the basal slip. Thus sometimes characteristicfracture surfaces are formed during stress corrosion cracking (SCC) or fatigue crack propagation (FCP) in Mgalloys, where many parallel lines are formed. These lines are different from so-called fatigue striations, becausethey are formed even under sustained load condition of SCC. Consequently, electron back scattered diffraction(EBSD) technique was applied on the fracture surface, and the formation mechanism of parallel lines wasinvestigated. EBSD-assisted fractography had revealed that the characteristic parallel lines were formed due tothe operation of basal slips, not twining. It is considered that hydrogen-enhanced localized plasticity (HELP)mechanism had been activated under corrosive environment

Corrosion fatigue behavior of extruded AZ80, AZ61, and AM60 magnesium alloys in distilled water

Rotary bending fatigue tests were conducted in laboratory air and distilled water using three extruded magnesium (Mg) alloys AZ80, AZ61, and AM60 with different chemical compositions. In laboratory air, thefatigue strengths at high stress levels were similar in all alloys because cracks initiated at Al-Mn intermetallic compounds, whereas AZ80 with the largest Al content exhibited the highestfatigue strength at low stress levels, which was attributed to the crack initiation due to cyclic slip deformation in the matrix microstructure. In distilled water, fatigue strengths were considerably decreased due to theformation of corrosion pits in all alloys, and the difference of fatigue strength at low stress levels among the alloys disappeared, indicating that the addition ofAl that improved the fatigue strength in laboratory air was detrimental to corrosion fatigue.С использованием методики сварки трения были получены соединения двух алюмини­евых сплавов: литого (АС4СН-Т6) и обрабо­танного давлением (А6061-Т6). Исследова­лось влияние микроструктуры и послетепературной обработки на сопротивление усталости различных сварных соединений. Центральная часть зоны сварки характери­зуется более низкими значения твердости по Виккерсу, чем зоны основных металлов, при­ чем минимальные значения твердости были зафиксированы на пути перемещения сва­рочного инструмента. Статическое разруше­ние сварных соединений при растяжении имело место со стороны основного сплава А6061, где твердость была минимальна, при­ чем статическая прочность сварного соеди­нения из разнородных сплавов была ниже, чем у сплавов АС4СН и А6061. Усталостное разрушение имело место для основного сплава АС4СН, что связано с наличием в нем литейных дефектов, причем усталостная прочность сварного соединения из разнород­ных сплавов оказалась такой же, как сплава АС4СН, но ниже, чем сплава А6061. При­ менение методики сварки трением и после- температурной обработки позволило повы­сить усталостную прочность сварных соеди­нений разнородных сплавов до уровня основного сплава А6061

Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys

Cast aluminum alloy, AC4CH-T6, and wrought aluminum alloy, A6061-T6, werejoined by means of friction stir welding (FSW) technique. The effect of microstructure and post heat treatment on fatigue behavior of the dissimilar joints was investigated. Near the weld centre, Vickers hardness was lower than in the parent metals and the hardness minima were observed along the trace route ofFSW tool’s shoulder edge. Tensilefracture tookplace on A6061 side where the hardness was minimal, resulting in the lower static strength of the dissimilar joints than AC4CH or A6061. Fatigue fracture occurred on AC4CH side due to casting defects and the fatigue strength of the dissimilarjoints was similar to that of AC4CH, but lower than that of A6061. Friction stirprocess (FSP) andpost heat treatment successfully improved thefatigue strength of the dissimilarjoints up to that of the parent metal, A6061.Испытания на круговой изгиб для оценки сопротивления усталости проводили на воз­духе и в дистиллированной воде на трех экструзивных магниевых сплавах AZ80, AZ61 и AM60 различного химического сос­тава. На воздухе сопротивление усталости при высоких уровнях напряжений было при­ мерно одинаковым для всех сплавов, по­скольку трещины зарождались у интерме­таллических соединений Al-Mn, тогда как AZ80 с наибольшим содержанием Al имел наибольшее сопротивление усталости при низких уровнях напряжений, что объясня­ется зарождением трещин вследствие циклической деформации скольжения в микро­структуре матрицы. В дистиллированной воде сопротивление усталости значительно снижалось за счет образования коррозион­ных язв во всех сплавах, а различие в сопротивлении усталости при низких уров­ нях напряжений отсутствовало, указывая на то, что добавка Al, улучшавшая сопротив­ление усталости на воздухе, оказывала отрицательное воздействие на коррозион­ную усталость