Grain boundary phase equilibrium in metallic systems. Final report, December 1, 1986--May 31, 1991

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Characterization of intergranular cuprous oxide in polycrystalline YBa2Cu3O7-x

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106466 ◽

1988 ◽

Vol 46 ◽

pp. 880-881

Author(s):

Bradley L. Thiel ◽

Chan Han R. P. ◽

Kurosky L. C. Hutter ◽

I. A. Aksay ◽

Mehmet Sarikaya

Keyword(s):

Grain Boundary ◽

Cuprous Oxide ◽

Room Temperature ◽

Boundary Phase ◽

Spectroscopic Techniques ◽

Transition Width ◽

Practical Applications ◽

Thin Foils ◽

Superconducting Oxides

The identification of extraneous phases is important in understanding of high Tc superconducting oxides. The spectroscopic techniques commonly used in determining the origin of superconductivity (such as RAMAN, XPS, AES, and EXAFS) are surface-sensitive. Hence a grain boundary phase several nanometers thick could produce irrelevant spectroscopic results and cause erroneous conclusions. The intergranular phases present a major technological consideration for practical applications. In this communication we report the identification of a Cu2O grain boundary phase which forms during the sintering of YBa2Cu3O7-x (1:2:3 compound).Samples are prepared using a mixture of Y2O3. CuO, and BaO2 powders dispersed in ethanol for complete mixing. The pellets pressed at 20,000 psi are heated to 950°C at a rate of 5°C per min, held for 1 hr, and cooled at 1°C per min to room temperature. The samples show a Tc of 91K with a transition width of 2K. In order to prevent damage, a low temperature stage is used in milling to prepare thin foils which are then observed, using a liquid nitrogen holder, in a Philips 430T at 300 kV.

Magnetic properties evolution with grain boundary phase transformation and their growth in Nd-Fe-Cu-Ga-B sintered magnet during post-sinter annealing process

Intermetallics ◽

10.1016/j.intermet.2021.107303 ◽

2021 ◽

Vol 137 ◽

pp. 107303

Author(s):

Song Fu ◽

Xiaolian Liu ◽

Jiaying Jin ◽

Zhiheng Zhang ◽

Yongsheng Liu ◽

...

Keyword(s):

Magnetic Properties ◽

Phase Transformation ◽

Grain Boundary ◽

Annealing Process ◽

Boundary Phase ◽

Sintered Magnet

Density-based grain boundary phase diagrams: Application to Fe-Mn-Cr, Fe-Mn-Ni, Fe-Mn-Co, Fe-Cr-Ni and Fe-Cr-Co alloy systems

Acta Materialia ◽

10.1016/j.actamat.2021.116668 ◽

2021 ◽

Vol 207 ◽

pp. 116668

Author(s):

Lei Wang ◽

Reza Darvishi Kamachali

Keyword(s):

Grain Boundary ◽

Phase Diagrams ◽

Boundary Phase ◽

Alloy Systems

Quasi-crystalline grain-boundary phase in the magnesium die-cast alloy ZA85

Scripta Materialia ◽

10.1016/s1359-6462(01)01052-1 ◽

2001 ◽

Vol 45 (5) ◽

pp. 517-524 ◽

Cited By ~ 57

Author(s):

M Vogel ◽

O Kraft ◽

G Dehm ◽

E Arzt

Keyword(s):

Grain Boundary ◽

Cast Alloy ◽

Boundary Phase ◽

Die Cast

Grain Boundary Phase Segregation for Dramatic Improvement of the Thermoelectric Performance of Oxide Ceramics

ACS Applied Materials & Interfaces ◽

10.1021/acsami.8b12710 ◽

2018 ◽

Vol 10 (45) ◽

pp. 39018-39024 ◽

Cited By ~ 9

Author(s):

Xueyan Song ◽

Sergio A. Paredes Navia ◽

Liang Liang ◽

Cullen Boyle ◽

Cesar-Octavio Romo-De-La-Cruz ◽

...

Keyword(s):

Grain Boundary ◽

Phase Segregation ◽

Thermoelectric Performance ◽

Boundary Phase ◽

Dramatic Improvement ◽

Oxide Ceramics

Microstructure and Magnetic Properties of NdFeB Sintered Magnets Diffusion-Treated with Cu/Al Mixed Dyco Alloy-Powder

Archives of Metallurgy and Materials ◽

10.1515/amm-2017-0189 ◽

2017 ◽

Vol 62 (2) ◽

pp. 1263-1266 ◽

Cited By ~ 7

Author(s):

M.-W. Lee ◽

K.-H. Bae ◽

S.-R. Lee ◽

H.-J. Kim ◽

T.-S. Jang

Keyword(s):

Grain Boundary ◽

Diffusion Path ◽

Boundary Phase ◽

Core Shell ◽

Phase Layer ◽

Sintered Magnets ◽

The Core ◽

Shell Type ◽

Property Changes ◽

And Diffusion

AbstractWe investigated the microstructural and magnetic property changes of DyCo, Cu + DyCo, and Al + DyCo diffusion-treated NdFeB sintered magnets. The coercivity of all diffusion treated magnet was increased at 880ºC of 1stpost annealing(PA), by 6.1 kOe in Cu and 7.0 kOe in Al mixed DyCo coated magnets, whereas this increment was found to be relatively low (3.9 kOe) in the magnet coated with DyCo only. The diffusivity and diffusion depth of Dy were increased in those magnets which were treated with Cu or Al mixed DyCo, mainly due to comparatively easy diffusion path provided by Cu and Al because of their solubility with Ndrich grain boundary phase. The formation of Cu/Al-rich grain boundary phase might have enhanced the diffusivity of Dy-atoms. Moreover, relatively a large number of Dy atoms reached into the magnet and mostly segregated at the interface of Nd2Fe14B and grain boundary phases covering Nd2Fe14B grains so that the core-shell type structures were developed. The formation of highly anisotropic (Nd, Dy)2Fe14B phase layer, which acted as the shell in the core-shell type structure so as to prevent the reverse domain movement, was the cause of enhancing the coercivity of diffusion treated NdFeB magnets. Segregation of cobalt in Nd-rich TJP followed by the formation of Co-rich phase was beneficial for the coercivity enhancement, resulting in the stabilization of the metastable c-Nd2O3phase.

Effect of rare-earth species on the wear properties of α sialon and β silicon nitride ceramics under tribochemical type conditions

Journal of Materials Research ◽

10.1557/jmr.2004.0357 ◽

2004 ◽

Vol 19 (9) ◽

pp. 2750-2758 ◽

Cited By ~ 6

Author(s):

Mark I. Jones ◽

Kiyoshi Hirao ◽

Hideki Hyuga ◽

Yukihiko Yamauchi

Keyword(s):

Rare Earth ◽

Grain Boundary ◽

Wear Behavior ◽

Rare Earth Oxide ◽

Lower Amount ◽

Boundary Phase ◽

Wear Properties ◽

Sintering Additives ◽

Nitride Ceramics ◽

Worn Surfaces

The wear properties under low loads of β Si3N4 and α sialon materials sintered with different rare-earth oxide sintering additives have been studied under dry sliding conditions using block-on-ring wear tests. All the worn surfaces showed an absence of fracture and smooth surfaces with the presence of an oxygen-rich filmlike debris indicating tribochemically induced oxidation of the surfaces. Extensive grain boundary removal was observed on the worn surfaces thought to be due to adhesion between this silicate phase and the tribochemically oxidized surfaces. The resistance to such oxidation and the properties of the residual grain boundary phase are thought to be important parameters affecting the wear behavior under the present testing conditions. For both the β Si3N4 and α sialon materials, there was an increase in wear resistance with decreasing cationic radius of the rare earth, thought to be due to improved oxidation resistance, and this was more remarkable in the case of the sialon materials where the incorporation of the sintering additives into the Si3N4 structure results in a lower amount of residual boundary phase.