Activation Mechanism and Infiltration Kinetic for Pressureless Melt Infiltration of Ti Activated Al₂O₃ Preforms by High Melting Alloy

Abstract

Metal matrix composites (MMC) represent a class of materials of broad technological and commercial significance designed for applications where the contrasting material properties of both metals and ceramics are needed. [1] MMC combine the high strength and wear resistance of ceramics with the ductility as well as the thermal and electrical conductivity of metals. The ceramic phase within the metal matrix guarantees a failure-tolerant behavior and low thermal expansion. [2] Many fabrication routes have been described in previous studies, [3] the most important ones are pressureless and pressure assisted metal melt infiltration techniques as well as powder metallurgical methods. The choice of a suitable manufacturing route is conditioned by cost factors, form flexibility and production temperature, [3,4] For certain applications in the food, pharmaceutical and automotive industry, the required properties are best met by composites made of alumina (Al 2 O 3 ) and high-melting Fe-based alloys (>1400 8C) such as X3CrNi13-4. [5][6][7][8][9] Pressureless infiltration would be the manufacturing route of choice for many of these applications, but the alumina-steel system lacks an important prerequisite, that makes infiltration without pressure possible: Oxide ceramics in general, due to their ionic character, show bad wettability by metal melts. The equilibrium contact angle u Y , which depends on the surface tensions of the phases involved, is given by Young's equation [10][11][12] (Eq. 1):and is in general well over 908 for such systems. [13][14][15][16] It is therefore not surprising that steel melts do not wet alumina surfaces.Pressure assisted infiltration and previous activation of the metal and/or the ceramic preform by incorporating reactive metals like titanium (Ti) are the two methods at disposal to circumvent the wettability problem. [2,7] Moreover, it was shown that a pressure drop within preforms, caused by the reaction of reactive metals such as e.g. Ni, Ti or Al and thus generation of a vacuum atmosphere is favorable for successful infiltration. [17] Applying pressure to the melt allows overcoming the negative capillary forces, but the pressurizing systems are technically demanding. The addition of a reactive element such as Ti enhances the infiltration performance either by lowering the surface tension of the metal melt and/or by the reactive modification of the ceramic surface. [18] It is well known that the addition of Ti to brazing solders for joining ceramic components lowers the contact angle of the metal melt with alumina due to the formation of a reactive layer. [19,20] Addition of titanium to steel melts lowers the surface tension, although there is a large spread in the data which are due to the presence or absence of surface active species in the gas phase. The formation of a TiO x reactive layer, and also modification of fluid flow and active metal adsorption are additional mechanisms that have been postulated to enhance wettability. [21,22] The activator may be prealloyed into the metal or dis...

Bonding mechanism of X10CrNi18-8 with Ni/Al2O3 composite ceramic by pressureless infiltration

“…H=R/2·{[(P 1 +(2·σ·cosθ)/R)·τ]/η} 1/2 (4) where H is the infiltration depth, R is the capillary radius, P 1 is the vacuum suction force, σ is the liquid metal surface tension, θ is the contact angle, τ is the dwell time, and η is the liquid metal viscous value. It can be concluded from Eq.…”

“…So, pressureless infiltration may be a better choice, which relies on the wettability between ceramic and metal melts [3]. But the contact angle between the steel melt and oxide ceramics still remains above 90° at 1 600 °C [4]. This poor wettability was improved by Ti-activated infiltration [1−4] or coating metal layers (e.g.…”

“…Among various MMCs, high-melting alloy steel matrix composites reinforced by oxide ceramics (e.g. Al 2 O 3 and ZrO 2 ) not only have various advantages of MMCs but also possess ideal performance at high temperature, which have been produced by melts infiltration [1][2][3][4][5][6][7][8][9] and tape casting [10]. In comparison with the tape casting, the melts infiltration is a more economic and attractive method.…”

Processing and mechanical properties of three-dimensional network alumina ceramic/alloy steel composites

“…This failure can be explained by two reasons: (1) The structure of traditional porous ceramics are usually bending pore-walls and thin struts (foaming method), or hollow struts (polymer precursor method); (2) the softening effect brought on by the higher infiltration temperature and the pressing effect created by the high density of steel melts are inevitable factors. In addition, the poor interface bonding behavior between ceramics and alloy steel is a well-known problem [8][9]. So, it becomes very interesting for the fabrication of new ceramic network skeletons with the high-temperature structural stability and 3-D network ceramic/steel MMCs with an excellent bonding interface.…”

Conductive TiC/Ti–Cu/C composites fabricated by Ti–Cu alloy reactive infiltration into 3D-printed carbon performs

“…During the last decades, several processing routes were developed in order to decrease production costs and achieve adequate properties of advanced MMCs. [1][2][3] High temperature, hard MMCs with a wide range of compositions and controlled microstructure can be produced by compaction and forming of metal-ceramic powders. [4][5][6] Kaftelen et al 4 produced Al-Cu matrix composites reinforced with TiC particulates by two distinct routes: mechanical alloying and flux-assisted casting of TiC and Al-4 wt.% Cu alloy mixtures.…”