Qinling Bi

The Tribological Behavior of a Ti-46Al-2Cr-2Nb Alloy Under Liquid Paraffine Lubrication

The tribological behavior of a Ti-46Al-2Cr-2Nb alloy prepared by hot-pressed sintering was investigated under liquid paraffine lubrication against AISI 52100 steel ball in ambient environment and at varying loads and sliding speeds. For comparison, the tribological behavior of a common Ti-6Al-4V alloy was also examined under the same testing conditions. The worn surfaces of the two alloys were analyzed using a scanning electron microscope. The friction coefficient of the Ti-46Al-2Cr-2Nb alloy in the range of 0.13–0.18 was significantly lower than that of the Ti-6Al-4V alloy (0.4–0.5), but comparable to that under dry sliding, which indicated that TiAl intermetallics could be more effectively lubricated by liquid paraffine than titanium alloys. Applied load and sliding speed have little effect on the friction coefficient of the Ti-46Al-2Cr-2Nb alloy. The wear rate of the Ti-46Al-2Cr-2Nb alloy was about 45–120 times lower than that of Ti-6Al-4V alloy owing to Ti-6Al-4V alloy could not be lubricated effectively. The wear rate of the Ti-46Al-2Cr-2Nb alloy increased with increasing applied load, but decreased slightly at first and then increased with increasing sliding speed. The wear mechanism of the Ti-46Al-2Cr-2Nb intermetallics under liquid paraffine lubrication was dominated by main plowing and slight flaking-off, but that of the Ti-6Al-4V alloy was plastic deformation and severe delamination.

Nanostructured Hypoeutectic Fe-B Alloy Prepared by a Self-propagating High Temperature Synthesis Combining a Rapid Cooling Technique.

We have successfully synthesized bulk nanostructured Fe94.3B5.7 alloy using the one-step approach of a self-propagating high temperature synthesis (SHS) combining a rapid cooling technique. This method is convenient, low in cost, and capable of being scaled up for processing the bulk nanostructured materials. The solidification microstructure is composed of a relatively coarse, uniformly distributed dendriteto a nanostructured eutectic matrix with α-Fe(B) and t-Fe2B phases. The fine eutectic structure is disorganized, and the precipitation Fe2B is found in the α-Fe(B) phase of the eutectic. The dendrite phase has the t-Fe2B structure rather than α-Fe(B) in the Fe94.3B5.7 alloy, because the growth velocity of t-Fe2B is faster than that of the α-Fe with the deeply super-cooling degree. The coercivity (Hc) and saturation magnetization (Ms) values of the Fe94.3B5.7 alloy are 11 A/m and 1.74T, respectively. Moreover, the Fe94.3B5.7 alloy yields at 1430 MPa and fractures at 1710 MPa with a large ductility of 19.8% at compressive test.

Combustion Synthesis and Characterization of Bulk Nanocrystalline

Bulk nanocrystalline Fe88Si12 alloy is fabricated by a combustion synthesis processing that is convenient, low in cost, and capable of being scaled up. The Fe88Si12 alloy consists of two phases: ¿-Fe(Si) and Fe3Si. It is a composite structure of meshwork dispersed in a matrix. The meshwork is a few micrometers in length and 0.5-1 ¿m in diameter, and the grain size of the matrix is in the range of 5-15 nm. The nanocrystalline Fe88Si12 alloy is yielded at 1760 MPa with a large ductility of 14.6% in compressive test. Moreover, the coercive force of the product is approximately 3.6 A/m and saturation magnetization is about 196 emu/g. The results suggest that the product exhibits good mechanical behavior and soft magnet properties.

{\bf Fe}_{\bf 88} {\bf Si}_{\bf 12}

The limited room temperature ductility of nanostructured materials with uniform grain size distribution restricts practical applications. To circumvent this problem, we employ a self-propagating high temperature synthesis combining a rapid solidification process to prepare the bulk nano-eutectic Fe83B17 alloy, which can lead to simultaneous high strength and large ductility. The microstructure of the Fe83B17 alloy has been examined in detail using x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The Fe83B17 alloy is composed of the eutectic of tetragonal Fe2B and α-Fe phases. The t-Fe2B and α-Fe phases display a fine lamellar eutectic structure with lamellar spacing of about 50 nm. The size of the eutectic colonies is in the range 3–25 µm. High yield strength (1089 MPa) and large ductility (~24.9%) are observed simultaneously in mechanical behaviour tests. The rotation of the eutectic colonies, accompanying viscosity plastic flows to release the localization of the shear stress, can contribute to the simultaneous high strength and large ductility.

Alloy

A bronze 663–11.7 wt% nickel-coated graphite composite was prepared by using a powder metallurgy route. Ttribological tests were carried out to investigate the effect of normal loads on a composite with a pin-on-disc tribotester at a constant sliding speed (0.083 m/s) in seawater. The nickel-coated graphite could smear out from the matrix and acted as a solid lubricant during the sliding process. When the normal load exceeded 110 N, the friction coefficient of the composite decreased, whereas the specific wear rate of the composite increased. The obtained results indicated that 110 N was a critical threshold of applied load at which there was a transition of friction and wear regimes of the bronze-nickel-coated graphite composite. When the applied load was <110 N, the wear mechanism of the composite was abrasive wear. However, the wear mechanism was abrasive wear and severe delamination when the normal load exceeded 110 N.

Microstructure and mechanical behaviour of nano-eutectic Fe83B17 alloy prepared by a self-propagating high temperature synthesis combining rapid solidification

There is an ongoing need for developing high temperature self-lubricating materials to meet the severe conditions of mechanical systems, such as advanced engines which require increasingly high working temperatures (at 1000 °C or above) and long life [1-7]. However, achieving and maintaining low friction and wear at high temperatures have been very difficult in the past and still are the toughest problems encountered in the field of tribology [8,9]. Yet, the efforts to explore novel high temperature self-lubricating materials possessing favorable frictional property and superior wear resistance abilities have never stopped. As a result, great strides have been made in recent years in the fabrication and diverse utilization of new high temperature self-lubricating materials that are capable of satisfying the multifunctional needs of more advanced mechanical systems [10-15]. The following tribological issues addressed in this chapter are presented:

Effect of Normal Loads on Tribological Properties of Bronze-Graphite Composite under Seawater Condition

Ni3Al matrix composites with various BaCrO4 contents were fabricated using a powder metallurgy technique and their tribological behavior was studied from room temperature to 800°C. The results show that at high temperature of about 800°C, the tribological properties of the composites were improved. However, it was found that BaCrO4 was absent but BaAl2O4 formed in the composite during the fabrication process. The low wear rate was attributed to the oxidative layer consisting of NiO and BaCrO4 that re-formed on the worn surface, which effectively protects the sliding surface from wear at high temperatures. On the whole, BaCrO4 can act as a solid lubricant for Ni3Al intermetallics at high temperatures.

High Temperature Self-Lubricating Materials

Sliding wear behaviour of nanocrystalline Fe88Si12 alloys with different grain sizes has been investigated under low load and speed. The friction coefficient of the Fe88Si12 alloy changes slightly with the grain size, but the wear resistance improves as the grain size decreases. The reduction of the grain size of the Fe88Si12 alloy not only results in the hardness increase, but also is beneficial to form Fe2SiO4 film on the worn surface. The Fe2SiO4 layer can form on the worn surface of the Fe88Si12 alloy even under smaller applied load when the grain size decreases.

Barium Chromate as a Solid Lubricant for Nickel Aluminum

Dry sliding wear behavior of nanocrystalline Fe88Si12 alloy has been investigated compared with coarse grained counterpart. The friction coefficient of the Fe88Si12 alloy changes slightly with grain size. But the wear resistance of the Fe88Si12 alloy improves as the grain size decreases to 40 nm, and then weakens when the grain size decreases from 40 nm to 10 nm. The grain size has significantly effect on the tribological behavior of Fe88Si12 alloy by modifying the hardness and the tribo-chemical interaction on the sliding zone during the wear process.

Sliding Wear Behaviour of Nanocrystalline Fe88Si12 Alloy Under Low Load and Speed

In this study, bulk nanostructured composite Cu60Fe40 alloy is prepared by a combustion synthesis technique. The prepared Cu60Fe40 alloy consists of Cu(Fe) solid solution and Fe(Cu) solid solution phases. The large-scaled compositional segregation in the Cu-rich and Fe-rich phases is not observed, respectively. A few micron-sized dendrite (Fe(Cu) solid solution) is embedded into the nanostructured matrix (Cu(Fe) solid solution). The grain size of the matrix is in the range 50–300 nm. The yield and fracture strength of the Cu60Fe40 alloy are 540 and 1050 MPa, respectively, and the fracture strain obtained from the compression test is about 20.9%. The Cu60Fe40 alloy displays notable work hardening in the compressive deformation.