Controlling Grain Size in Oxide Ceramics for Optimization of Strength and Wear Resistance

t is well known that alumina ceramics undergo a time dependent wear transition during sliding wear. The transition, which is associated with 1-2 orders of magnitude increase in specific wear rate, involves a change from mild wear to intergranular fracture. The transition is strongly grain size dependent, with the time to the transition decreasing with grain size. However, there is a minimum grain size that can be achieved in fully dense alumina using commercially viable processing. Alternative strategies for reducing grain size and increasing toughness are through the addition of a fine second phase, with SiC and ZrO2being the most promising. The resultant composite not only has finer grain size, but also exhibits additional toughening mechanisms. This paper reports on the microstructural control in alumina, zirconia toughened alumina and alumina-silicon carbide composites. The grain size and residual stress distribution are related to the damage accumulation mechanism that occur during frictional contact, in particular the surface specific dislocation activity.

Download Full-text

Sintering and Mechanical Properties of Alumina Ceramics Prepared by Nanosize Alumina

Materials Science Forum ◽

10.4028/www.scientific.net/msf.544-545.821 ◽

2007 ◽

Vol 544-545 ◽

pp. 821-824

Author(s):

Indra ◽

S.W. Oh ◽

Hee Joon Kim

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Relative Density ◽

Mechanical Characteristics ◽

Indentation Test ◽

Test System ◽

Alumina Ceramics ◽

New Materials ◽

Size Dependent

This work examined the mechanical properties of alumina that can directly be enhanced by ratio of nano sized alumina powders additives to micro size alumina powders (n/m ratio). These new materials have mechanical properties that are strongly grain size dependent and often significantly different from those of their coarser grained counter parts. The mechanical characteristics of samples were observed by using the indentation test system. This data shows that the relative density for the sample is increased with increasing Meyer hardness.

Download Full-text

Processing of Homogeneous Zirconia-Toughened Alumina Ceramics with High Dry-Sliding Wear Resistance

Journal of the American Ceramic Society ◽

10.1111/j.1151-2916.1999.tb02045.x ◽

2004 ◽

Vol 82 (8) ◽

pp. 2087-2093 ◽

Cited By ~ 44

Author(s):

Bas Kerkwijk ◽

Louis Winnubst ◽

Elmer J. Mulder ◽

Henk Verweij

Keyword(s):

Wear Resistance ◽

Sliding Wear ◽

Dry Sliding Wear ◽

Dry Sliding ◽

Alumina Ceramics ◽

Zirconia Toughened Alumina

Download Full-text

Modeling of Grain-Size-Dependent Microfracture-Controlled Sliding Wear in Polycrystalline Alumina

Journal of the American Ceramic Society ◽

10.1111/j.1151-2916.1993.tb07786.x ◽

1993 ◽

Vol 76 (9) ◽

pp. 2393-2396 ◽

Cited By ~ 38

Author(s):

Haiyan Liu ◽

Morris E. Fine

Keyword(s):

Grain Size ◽

Sliding Wear ◽

Polycrystalline Alumina ◽

Size Dependent

Download Full-text

The Preparation and Properties of Alumina Ceramics through a Two-Step Pressureless Sintering Process

Materials Science Forum ◽

10.4028/www.scientific.net/msf.922.47 ◽

2018 ◽

Vol 922 ◽

pp. 47-54

Author(s):

Chang Suo Yuan ◽

Zi Jing Wang ◽

Qiang Zhi ◽

Ya Ming Zhang ◽

Xu Dong Wang ◽

...

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Relative Density ◽

High Purity ◽

Dominant Factor ◽

Second Phase ◽

Pressureless Sintering ◽

Sintering Process ◽

Alumina Ceramics ◽

Soaking Time

In this paper, a high-dense alumina ceramics were prepared through the two-step pressureless sintering process with high-purity alumina powder as raw materials and high-purity MgO as sintering aids. The effects of the sintering temperature in the first-step (T1) and the soaking time (t) in the second sintering step (T2) on the density, microstructure and mechanical properties of the alumina ceramics were studied. The results indicated that the relative density increased with the increase of T1 temperature whereas it increased and then decreased with the increase of MgO content. Higher T1 temperature and extended soaking time caused larger grain size, which accompanied with the Ostwald ripening of the grain and led to non-uniformity of grain size distribution. The addition of MgO was beneficial to the decrease in grain size due to pinning effect of the second phase. For samples with shorter soaking time, sintering with higher T1 temperature led to better mechanical properties because of its high density. However, for the long soaking time, all samples after sintering at different T1 temperature were fully-densified, so the grain size become to the dominant factor of strength, thus samples with lower T1 temperature exhibited better mechanical properties due to the refinement grain. Excessive addition of MgO resulted in defects, by which the strength increased firstly and then decreased slightly with the increased MgO content. For the samples with 2.5wt.% MgO, the optimum condition for the two-step pressureless sintering was T1=1450°C and T2=1400°C for 20h, and the obtained sample achieved the relative density of 96% and the strength of 507±32MPa.

Download Full-text

Influence of Zirconia Content and Grain Size on Physical and Mechanical Properties of Zirconia Toughened Alumina Ceramics

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.143-144.485 ◽

2011 ◽

Vol 143-144 ◽

pp. 485-488 ◽

Cited By ~ 2

Author(s):

Bao Yu Du ◽

Bo Zhao ◽

Tie Lin Duan

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Physical And Mechanical Properties ◽

Composite Ceramic ◽

Alumina Ceramics ◽

Alumina Matrix ◽

Zirconia Toughened Alumina ◽

Better Than ◽

Zirconia Content

Physical and mechanical properties as well as microstructure of zirconia toughened alumina ceramics with different zirconia content were tested. The results show that the best physical and mechanical properties are obtained in sub-micron composite ceramic when zirconia content is 25%; while the physical and mechanical properties of nano-zirconia toughened alumina ceramics are far better than those of sub-micron zirconia toughened alumina ceramics. Therefore physical and mechanical properties of ceramics can be improved significantly by adding proper amount of zirconia into alumina matrix and refining zirconia particles.

Download Full-text

Structure of second phases in TiAl alloys containing Cr and B

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087197 ◽

1991 ◽

Vol 49 ◽

pp. 576-577

Author(s):

Ernest L. Hall ◽

Shyh-Chin Huang

Keyword(s):

Grain Size ◽

Second Phase ◽

Structure And Properties ◽

Tial Alloys ◽

Second Phases ◽

Interstitial Elements

Addition of interstitial elements to γ-TiAl alloys is currently being explored as a method for improving the properties of these alloys. Previous work in which a number of interstitial elements were studied showed that boron was particularly effective in refining the grain size in castings, and led to enhanced strength while maintaining reasonable ductility. Other investigators have shown that B in γ-TiAl alloys tends to promote the formation of TiB2 as a second phase. In this study, the microstructure of Bcontaining TiAl alloys was examined in detail in order to describe the mechanism by which B alters the structure and properties of these alloys.

Download Full-text

Effect of Rare Earth Ce on Deep Stamping Properties of High-Strength Interstitial-Free Steel Containing Phosphorus

Materials ◽

10.3390/ma13061473 ◽

2020 ◽

Vol 13 (6) ◽

pp. 1473

Author(s):

Hao Wang ◽

Yanping Bao ◽

Chengyi Duan ◽

Lu Lu ◽

Yan Liu ◽

...

Keyword(s):

Solid Solution ◽

Grain Size ◽

Rare Earth ◽

High Strength ◽

Rolling Process ◽

P Element ◽

Second Phase ◽

Strengthening Effect ◽

Interstitial Free ◽

If Steel

The influence of rare earth Ce on the deep stamping property of high-strength interstitial-free (IF) steel containing phosphorus was analyzed. After adding 120 kg ferrocerium alloy (Ce content is 10%) in the steel, the inclusion statistics and the two-dimensional morphology of the samples in the direction of 1/4 thickness of slab and each rolling process were observed and compared by scanning electron microscope (SEM). After the samples in each rolling process were treated by acid leaching, the three-dimensional morphology and components of the second phase precipitates were observed by SEM and energy dispersive spectrometer (EDS). The microstructure of the sample was observed by optical microscope, and the grain size was compared. Meanwhile, the content and strength of the favorable texture were analyzed by X-ray diffraction (XRD). Finally, the mechanical properties of the product were analyzed. The results showed that: (1) The combination of rare earth Ce with activity O and S in steel had lower Gibbs free energy, and it was easy to generate CeAlO3, Ce2O2S, and Ce2O3. The inclusions size was obviously reduced, but the number of inclusions was increased after adding rare earth. The morphology of inclusions changed from chain and strip to spherical. The size of rare earth inclusions was mostly about 2–5 μm, distributed and dispersed, and their elastic modulus was close to that of steel matrix, which was conducive to improving the structure continuity of steel. (2) The rare earth compound had a high melting point. As a heterogeneous nucleation point, the nucleation rate was increased and the solidification structure was refined. The grade of grain size of products was increased by 1.5 grades, which is helpful to improve the strength and plasticity of metal. (3) Rare earth Ce can inhibit the segregation of P element at the grain boundary and the precipitation of Fe(Nb+Ti)P phase. It can effectively increase the solid solution amount of P element in steel, improve the solid solution strengthening effect of P element in high-strength IF steel, and obtain a large proportion of {111} favorable texture, which is conducive to improving the stamping formability index r90 value.

Download Full-text

Effect of carbide grain size on microstructure and sliding wear behavior of HVOF-sprayed WC–12% Co coatings

Wear ◽

10.1016/s0043-1648(02)00294-6 ◽

2003 ◽

Vol 254 (1-2) ◽

pp. 23-34 ◽

Cited By ~ 205

Author(s):

Qiaoqin Yang ◽

Tetsuya Senda ◽

Akira Ohmori

Keyword(s):

Grain Size ◽

Sliding Wear ◽

Wear Behavior

Download Full-text

Machining and Wear of High-Alumina Ceramics for Structural Applications

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.409.137 ◽

2009 ◽

Vol 409 ◽

pp. 137-144 ◽

Cited By ~ 3

Author(s):

Stojana Veskovic-Bukudur ◽

Tanja Leban ◽

Milan Ambrozic ◽

Tomaž Kosmač

Keyword(s):

Grain Size ◽

Wear Rate ◽

Abrasive Wear ◽

Direct Relationship ◽

Bending Strength ◽

High Alumina ◽

Alumina Ceramics ◽

Large Area ◽

Structural Applications ◽

Worn Surfaces

The wear resistances of four standard-grade high-alumina ceramics were evaluated and related to their machining ability. Three of the material grades contained 96% of alumina and 4% of either calcium silicate, or magnesium silicate, or manganese titanate in the starting-powder composition. The nominal alumina content in the fourth material was 99.7%. The specimens were fabricated using a low-pressure injection-molding forming technique, followed by thermal de-binding and sintering. After sintering the four materials differ significantly in their grain size, bending strength and Vickers hardness. No direct relationship between the microstructural parameters and the mechanical properties was found, but there was a grain-size dependence of the surface finish after grinding under industrial conditions. The two silicate-containing ceramics exhibited considerably higher wear resistances than the two silicate-free ceramics, but no direct relationship between the abrasive wear rate during grinding and the cutting time was observed. The cutting ability represents a valuable material characteristic for industrial practice, but it should not be directly used for predicting the wear rate during grinding. Quantitative differences in the cutting time and abrasive wear rate were manifested in the different topographies of the worn surfaces. Cutting resulted in relatively large area fractions of plastically deformed surfaces, whereas pullouts dominated the worn surfaces after grinding.

Download Full-text