The equilibrium solidified phase diagrams of high boron high speed steel have been calculated and the vertical section of iron-carbon pseudo-binary phase diagrams has been drawn with different aluminum concentration. The effect of aluminum on phase diagrams and solidification microstructure has been investigated by using optical microscope, scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. The results show that the austenite region shrinks to a small area and the d-iron changes into a-iron directly during cooling process when the aluminum content reaches 1.5 wt.%. The addition of excessive amount of aluminum favors the formation of ferrite, which leads to the hardness decreasing. Moreover, excessive amount of aluminum (Al ! 1.5 wt.%) will make network M 2 B borocarbides tend to break. Alloying with aluminum raises the solubility of carbon in the matrix and reduces the quenched hardness. The calculation results are agreed with the ones from experimental. The calculation of phase diagrams method has been successfully used for the computation of phase equilibrium in the multi-component high boron high-speed steel system. The work provides a practical method for engineers and researchers in related areas.Keywords: High boron high speed steel / phase diagram calculation / aluminum / solidification / Thermo-Calc Schlü sselwö rter: Hochborhaltige Schnellarbeitsstä hle / PhasendiagrammBerechnungen / Aluminium / Erstarrung / Thermo-Calc
The ring-block tribological behavior of the graphite/Cu(G/Cu) composites and copper-coated graphite-graphite/Cu(CCG-G/Cu) were studied by observing the friction coefficient,wear rate,microstructure and morphogoly of the composites after friction experiments.SEM and TEM were used to character the micro-morphology and micro-structure of debris,friction surface and friction cross section of the composites.The results show that adding 20wt% copper-coated graphite could reduced the friction coefficient and wear rate of the composites.The micro-morphology and micro-structure show that the copper phase are undergo oxidation and plastic deformation under cyclic stress,results in abundant deformation area in copper-rich zones.Interlaminar shedding and intramolecular tearing occurs in graphite phase,and then laid flat on the friction surface,forming a friction film with higher integrity and reducing the friction coefficient of the composites.The TEM images of the friction cross section show that deformation zone is mainly composed of accumulation zone,drag zone and carbon film.The simulation of the friction process shows that the initial stage is mainly dominated by abrasive wear and adhesive wear.With the progress of the experiment,the exposed copper phase is oxidized and oxidative wear occurs,graphite is shed and transferred to the contact surface.In the later stage of the experiment,a complete friction film with high graphite content is formed on the contact surface,which is mainly dominated by fatigue wear.
To improve the combination of graphite and copper, the
friction
and wear of a graphite/copper composite with a high content of graphite
(50 wt %), copper-coated graphite were used to modify it. To observe
the distribution law of each phase in the material and the change
of composite surface structure after the friction and wear experiment,
scanning electron microscopy (SEM) and transmission electron microscopy
(TEM) were used to characterize the micro-structure, friction film,
debris, and friction cross section of the composites. The results
show that the large particle size of copper-coated graphite is anisotropic
in the material, which helps to form a friction film with a high graphite
content on the contact surface. TEM images of the friction film and
debris directly reflect the structure changes of graphite and copper
during friction; under normal load and shear force, interlamellar
detachment and interlamellar fracture of graphite occur, and its edge
is folded and crimped, resulting in the loss of an ordered state in
some regions, which results in the instability of crystal lattice
and the transition from an ordered to disordered state of graphite,
resulting in the (002) halo ring in FFT results. Severe plastic deformation
and oxidation reactions occur in copper, and copper oxides are formed,
forming a high-strength and smooth oxide film in the metal-rich area
and improving the wear resistance of the material. TEM images of the
friction section directly show that an inverted triangular deformation
zone is formed on the surface of the sample after friction and wear
experiments. The edge of the deformation zone is stepped, consisting
of a drag zone and an accumulation zone, and the surface of the contact
zone is covered by a carbon film.
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