The effect of temperature, matrix alloying and substrate coatings on wettability and shear strength of Al/Al2O3 couples

Abstract

A fresh approach has been advanced to examine in the Al/Al 2 O 3 system the effects of temperature, alloying of Al with Ti or Sn, and Ti and Sn coatings on the substrate, on contact angles measured using a sessile-drop test, and on interface strength measured using a modified push-off test that allows shearing of solidified droplets with less than 90 deg contact angle. In the modified test, the solidified sessile-drop samples are bisected perpendicular to the drop/Al 2 O 3 interface at the midplane of the contact circle to obtain samples that permit bond strength measurement by stress application to the flat surface of the bisected couple. The test results show that interface strength is strongly influenced by the wetting properties; low contact angles correspond to high interface strength, which also exhibits a strong temperature dependence. An increase in the wettability test temperature led to an increase in the interface strength in the low-temperature range where contact angles were large and wettability was poor. The room-temperature shear tests conducted on thermally cycled sessile-drop test specimens revealed the effect of chemically formed interfacial oxides; a weakening of the thermally cycled Al/Al 2 O 3 interface was caused under the following conditions: (1) slow contact heating and short contact times in the wettability test, and (2) fast contact heating and longer contact times. The addition of 6 wt pct Ti or 7 wt pct Sn to Al only marginally influenced the contact angle and interfacial shear strength. However, Al 2 O 3 substrates having thin (Ͻ1 m) Ti coatings yielded relatively low contact angles and high bond strength, which appears to be related to the dissolution of the coating in Al and formation of a favorable interface structure.

Effect of CaF2 on Interfacial Phenomena of High Alumina Refractories with Al Alloy

“…[6][7][8] Interfacial behavior of pure Al/Al 2 O 3 systems has been extensively studied in the past, primarily for composite applications. [9][10][11][12][13][14] However, the interfacial behavior of high alumina monolithic refractories is considerably different, and is changed in the presence of nonwetting agents, and it is difficult to interpret their behavior based on the findings from the pure system.…”

“…The effect of physical properties such as porosity, surface roughness, and particle sizes as well as the processing conditions on the interfacial behavior of refractories is well known. [10][11][12][13][14][15][16][17][18][20][21][22][23] However, the understanding of the effect of the chemical composition, and in particular the role of nonwetting additives on interfacial reactions of the Al-alloy/high alumina refractory, is limited and uncertain.…”

Effect of Silica on High-Temperature Interfacial Phenomena of Monolithic Refractories with Al Alloy

“…[6][7][8] Interfacial behavior of pure Al/Al 2 O 3 systems has been extensively studied in the past, primarily for composite applications. [9][10][11][12][13][14] The interfacial behavior of Al alloys with the SiO 2 -Al 2 O 3 system is considerably different and cannot be clearly understood based on the results of the pure system. While the effects of physical properties such as porosity, surface roughness, particle sizes, and processing conditions on the interfacial behavior of refractories have been extensively studied, [10][11][12][13][14][15][16][17][18][20][21][22][23] an understanding of the effect of chemical composition on interfacial reactions of the Al-alloy/monolithic refractory system is far from complete.…”

“…[30,31] This is practically difficult to achieve under normal experimental conditions. A variety of approaches are often used to study the interfacial behavior of the Al-Al 2 O 3 system, namely, using high vacuum, high temperatures, or mechanical dosing techniques, [10][11][12][30][31][32][33][34][35][36][37] and the reported contact angles have been observed to range widely from 70 to 140 deg [9][10][11][12][13][14]18] because each method has its own merits in reducing the extent of the effect of the oxide layer. The presence of Mg, Ti, and Zr in the alloy can also lower the contact angle with alumina.…”

Current-Activated, Pressure-Assisted Infiltration: A Novel, Versatile Route for Producing Interpenetrating Ceramic–Metal Composites

“…[8] Therefore, numerous methods have been used to enhance the wettability. These methods include modifying the ceramic surface, [9] tailoring the chemistry of the metals and alloys, [9,10] the use of controlled atmospheres [10,11] and much higher temperatures than the melting points of the metals/alloys. [12] However, the components of the composites may be degraded due to chemical attack or introduction of new reaction phases at high temperatures.…”