Zr-rich Particles Research Articles

The effect of zirconium addition on microstructure and properties of ball milled and hot compacted powder of Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu alloy

Elemental powders of the composition Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu with addition of 1 and 2 wt% Zr were ball milled in a planetary high-energy ball mill and then hot pressed in vacuum under 600 MPa pressure at 380 °C. The effect of ball milling and hot pressing on the microstructure was investigated by means of X-ray diffraction measurements (XRD), light microscopy, analytical and scanning transmission electron microscopy (TEM). Ball milling for 80 h leads to homogenous, highly deformed microstructure of aluminium solid solution with grain size below 100 nm. In the powder with zirconium addition, some part of the Zr atoms diffused in aluminium up to 0.3 wt% Zr. The remaining was found to form Zr-rich particles identified as face centered cubic (fcc) phase. Good quality samples without pores and cracks obtained by hot pressing composed of grains and subgrains of size below 200 nm. The particles of MgZn 2 phase were identified which were located mainly between compacted particles of milled powder. Hot pressed powder showed Vickers microhardness of about 195 HV (0.2 N) and ultimate compression strength in the range 611–658 MPa in the compression test. Addition of zirconium had no influence on the strength of the compacted powders.

Investigation of the Precipitation in Mg-Zr Alloys

The Mg-Zr alloys with the Zr contents of 0.2%, 0.4%, 0.6% and 0.8% were prepared using induction melting, metal mold centrifugal casting process. The microstructures of the alloys were analyzed by scanning electron microscope, energy spectrum analysis, transmission electron microscope and their mechanical properties were also measured with tensile test. The results show that there are many micro- and nano-sized Zr-rich or Zr particles dispersed in Mg-Zr alloys. The nano-sized Zr-rich particle consists of a rectangle shaped Zr core and its surrounding Mg (Zr) solid solution shell with round exterior; a single Zr particle appears a coherent lattice relationship with matrix.

TEM and HRTEM studies of ball milled 6061 aluminium alloy powder with Zr addition

The effect of mechanical alloying on the microstructure of atomized 6061 aluminium alloy powder and 6061 powder with a zirconium addition was studied in the work. The atomized 6061 aluminium alloy powder and 6061 powder with addition of 2 wt.% Zr were milled in a planetary ball mill and investigated using X-ray diffraction measurements, conventional and high-resolution electron microscopy (TEM/HRTEM) and high-angle annular dark field scanning transmission electron microscopy combined with energy dispersive X-ray microanalysis. An increase of stresses was observed in milled powders after the refinement of crystallites beyond 100 nm. In the powder with zirconium addition, some part of the Zr atoms diffused in aluminium forming a solid solution containing up to 0.5 wt.% Zr. The remaining was found to form Zr-rich particles containing up to 88 wt.% Zr and were identified as face centred cubic (fcc) phase with lattice constant a= 0.48 nm. That fcc phase partially transformed into the L1(2) ordered phase. Eighty-hour milling brought an increase of microhardness (measured with Vickers method) from about 50 HV (168 MPa) for the initial 6061 powder to about 170 HV (552 MPa). The addition of zirconium had no influence on the microhardness.

Microstructure and properties of hot compacted powders of aluminium alloys

Atomized 6061 aluminium alloy powders with and without the addition of 2 wt% Zr were milled for 80 h in a planetary ball mill and hot pressed in vacuum. The milled powders showed microhardness of about 170 HV, which increased after hot pressing up to 260 HV and up to 280 HV for powders without and with the Zr additions, respectively. Compression tests showed the high yield stress of 300 MPa obtained for the hot-pressed sample produced from the initial powders compared with ultimate compression strength of above 800 MPa for that of the milled sample and slightly higher for that with Zr additions. The effect of hot pressing on the structure of powders was investigated using a conventional analytical and high-resolution electron microscopy and high angle annular dark-field scanning transmission electron microscopy combined with energy dispersive X-ray microanalysis. The samples of initial powders hot pressed in vacuum showed a cell structure with particles of the Mg(2)Si and AlFeSi phases in intercell areas. In the milled and hot-pressed sample, the homogeneous structure of small grains of size below 200 nm was observed. The AlFeSi and Mg(2)Si particles with size 20-100 nm were uniformly distributed as well as the Zr rich particles in the Zr containing alloy. The Zr-rich particles containing up to 80 at% Zr were identified as a metastable fcc cubic phase with lattice parameter a= 0.48 nm.

Diffusion behavior in an interface between U–10Zr alloy and HT-9 steel

The diffusion behavior in an interface between a U–10 wt.%Zr alloy and HT-9 steel at 700 °C and 730 °C was investigated. The Zr-rich layer near the interface between two alloys was formed mainly due to the decomposition of the δ-UZr 2 phase in U–Zr alloy, and acted to interrupt the interdiffusion of the alloying elements. Considerable interdiffusion was observed only when the Zr-rich layer was destroyed locally. As a result, the diffusion–reaction layer was mainly composed of a U-rich, (U,Zr)(Fe,Cr) 2 compound, Zr-rich and Zr-depleted layers. Fe elements which had diffused from HT-9 were mainly observed in the boundaries of the Zr-rich particles in the U–Zr alloy.

Effect of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y magnesium alloy

The influence of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y (wt.%) magnesium alloy was investigated. The grain size of alloys decreased with Zr content from 0% to 0.93% (wt.%). The addition of Zr greatly improved the ultimate tensile strength (UTS) and the elongation (EL), while slightly improved the tensile yield strength (TYS). The UTS and the EL of the alloy containing 0.93% Zr increased by 125.8 MPa and 6.96% compared with base alloy, respectively. The corrosion resistances were found to decrease with Zr content from 0% to 0.42% and then increase from 0.42% to 0.93%. The differences in the sizes and distributions of the Zr-rich particles have significant effects on the corrosion behaviors. The alloy with 0.42% Zr addition revealed the optimum combination of mechanical properties and corrosion resistance.

Existing form and effect of zirconium in pure Mg, Mg-Yb, and Mg-Zn-Yb alloys

The existing form and grain refining effects of small zirconium addition in pure Mg, Mg-Yb and Mg-Zn binary alloys, and Mg-Zn-Yb ternary alloy (ZK60-Yb) were investigated. The results show that Zr element exists mainly in single and cluster particles of pure α-Zr or Zn-Zr compounds inside grains and at grain boundaries. Only the particles located in the interior of grains can act as the nucleus for α-Mg growth and effectively promote the formation of fine equiaxed grains. The broken and dispersed Zr-rich particles produced during the hot extrusion process can form nebulous banded structure in which these fine particles may act as obstacles to dislocation motion in wrought magnesium alloys.

Pinning centres in NEG-123 active at liquid oxygen temperature (90.2 K)

We present a new type of (Nd,Eu,Gd)Ba2Cu3Oy ‘NEG-123’ material for superconducting permanent magnets for use at liquid oxygen temperature(90.2 K). This material exhibits an exceptionally high flux pinning up to the close vicinity ofTc. The improvement of the flux pinning was achieved by externally added ball-milledsecondary phase particles that partially transformed during the technological process to anew type of nanometre-scale Zr-rich particles. The critical current density improved by oneorder of magnitude at 77 and 90 K as compared to those of other RE-123 type materials.The exceptional trapped field at 90.2 K enabled a levitation experiment at liquid oxygentemperature, which proved that these materials can be used as superconducting permanentmagnets at 90 K. We point out that this technology can be easily adapted for massproduction.

Superplasticity in a Fine-Grained Mg—Zn—Y—Zr Alloy Containing Quasicrystalline Particles

A Mg–Zn–Y–Zr alloy sheet containing icosahedral quasicrystalline particles and Zr-rich particles has been developed by the thermomechanical processes, i.e. hot extrusion and hot rolling. The grain size is found to be 5 mm. The superplastic deformation behavior of the alloy has been investigated. Under the test condition in the strain rate range of 5 � 10 � 4 to 5 � 10 � 2 s � 1 and the temperature range between 300 � C and 450 � C, large elongation to failures are observed, especially around 600% at 450 � C( 5 � 10 � 4 s � 1 ). During superplastic deformation, the concurrent grain growth rate is significantly retarded by the presence of I-phase particles, thermally stable at the temperature up to around 500 � C. In addition, the formation of cavities is found to be negligible because of interfacial coherency between icosahedral quasicrystalline particles and the � -Mg matrix. Although superplastic deformation could be relatively prevented by the pinning effect of the distributed particles, microstructure stability can provide large elongation to failure in such an alloy.

Zirconium-enriched particles in spray-deposited Ni 3Al-based alloys

Ni{sub 3}Al is an ordered compound with potential high temperature applications. Recent results have shown that zirconium is an effective element in increasing the creep resistance of Ni{sub 3}Al-based alloys. Microalloying with Zr has also been reported to improve the ductility of Ni{sub 3}Al-based alloys. Chiba et al. proposed that Zr acts as a scavenger of harmful impurities when added in small amounts, while Gu et al. suggested that Zr increases the grain boundary cohesion of Ni{sub 3}Al alloys. In the case of spray-deposited nickel aluminides, Rautioaho and Saven found Zr-rich inclusions to exist in as-deposited alloys. After thermomechanical treatments of these alloys, Zr-rich precipitates similar to the above inclusions were sometimes observed. SEM/EDS studies showed that all inclusions contained nitrogen and some of them also oxygen. Moreover, a minor fraction of particles were enriched in sulphur up to a concentration of 25 at.%. In addition, SEM/WDS analyses revealed that a high fraction of Zr-rich particles had a small sulphur content of 0.5 to 1 at.%. In the present investigation, the character of Zr-enriched particles was clarified by additional analyses in SEM/EDS and STEM, and by high pulse count x-ray diffraction scans.

An EFTEM and conical dark field investigation of co-sputtered CoPt+Yttria stabilized zirconia thin films

Energy filtering transmission electron microscopy (EFTEM) using the Gatan Imaging Filter in a Philips CM20/STEM has been applied to co-sputtered CoPt+yttria stabilized zirconia (YSZ) thin films to determine the elemental distribution in as-deposited and annealed samples. Using the ZrN 23, CoM 23 and PtO 23 edges, jump ratio images have been recorded under rocking beam illumination. While the jump ratio images of the as-deposited film show nearly homogeneous contrast, the jump ratio images of the annealed film show clearly resolved Zr-rich particles with a mean size of 3 nm in a matrix of CoPt alloy. Conically scanned (hollow cone) dark field TEM images were also obtained to determine the volume fraction of L1 0 atomically ordered phase present in the CoPt matrix. By this technique we have determined that the ordered volume fraction is 0.4±0.1. These two, complementary techniques are powerful tools which can expand the usefulness of conventional TEM microscopes to encompass a wide variety of current materials science problems.

Effect of liquation on welding of a continuous cast sheet of an Ni 3Al alloy containing Zr

Autogenous gas tungsten arc welding was performed on a continuous cast sheet (about 1 mm thick) of an Ni 3Al alloy (Ni 77.83Al 21.73Zr 0.34B 0.10) known as IC-50. The material was highly susceptible to cracking in the heat-affected zone (HAZ). The cracks in the HAZ were liquation cracks and occurred along the grain boundaries. There were occasional solidification cracks in the fusion zone (FZ) and they occurred along the main dendrite boundaries. Microporosities were observed in both the FZ and HAZ. Microprobe analysis showed Zr enrichment in HAZ regions where melting had taken place. Annealing the alloy at 1100 °C for 5 h produced Zr-rich particles. Welding after the annealing showed similar behavior to that without annealing, except that the partially molten region in the HAZ was reduced in size. The role of Zr segregation at the grain boundaries in causing partial melting is discussed.