A. Mohammadnejad

info

Please Note

<p>This page displays the records of the person named above and is not linked to a unique person identifier. This record may need to be merged to a profile.</p>

Journal article (3)

3 records found

Spark plasma sintering of Ni ₃ Al-xB-1wt% CNT (0.0 < x < 1.5 at%) nanocomposite

Journal article (2019) - A. Mohammadnejad, A. Bahrami, M. Sajadi, M. Yazdan Mehr

This paper investigates the effects of carbon nanotubes (CNT) addition on the structure and mechanical properties of Ni ₃ Al-xB (0.0 < x < 1.5 at%) intermetallic compound. Ni ₃ Al-xB-1wt%CNT nanocomposite powders were first synthesized by mechanical alloying. Effects of CNT addition on the lattice strain and crystallite size of synthesized powders were investigated by means of X-ray diffraction (XRD) analysis. Scanning electron microscope (SEM) was used to study powder morphologies. Powders, synthesized by mechanical alloying, were then consolidated using spark plasma sintering (SPS), conducted at 950 °C under pressure 50 MPa. Microhardness and shear punch tests were employed to study the mechanical properties of sintered samples. Results show that CNT addition is accompanied by a decrease in crystallite size and a significant improvement of mechanical properties of Ni ₃ Al-xB (0.0 < x < 1.5 at%) intermetallic compounds. ...

Wear induced failure of automotive disc brakes

A case study

Journal article (2019) - Ali Mohammadnejad, Abbas Bahrami, Majid Goli, Hossein Dehbashi Nia, Peyman Taheri

This paper investigated a failure in a ventilated disc brake in an automobile. The failed brake disc had been in service for approximately 10 years. The observed failure was in the form of radial cracks that appeared to have initiated at the outer edge of the disc brake. The cracks were rather straight with no branching. Optical microscope, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to study the microstructure of the failed disc. Vickers microhardness test was also used to evaluate the hardness of the samples. Results showed that the root cause of crack formation, in this case, was related to the excessive wear in the brake disc. Different wear mechanisms, namely abrasive and adhesive wear, were recognized in the failed specimen. Moreover, the worn surface in some areas was covered with fine oxide particles. These particles appeared to have a significant contribution toward abrasion. To further understand the wear mechanisms, pin-on-disc experiments were also conducted on the samples. Results of the pin-on-disc experiments were compared and correlated to the results obtained from the failed brake disc. ...

Microstructure and mechanical properties of spark plasma sintered nanocrystalline Ni₃Al-xB (0.0<x<1.5 at%) alloy

Journal article (2018) - A. Mohammadnejad, A. Bahrami, M. Sajadi, P. Karimi, H. R. Fozveh, M. Yazdan Mehr

This study aims at studying the microstructure and mechanical properties of nanocrystalline Ni₃Al-xB (0.0<x<1.5 at%) alloy, made by mechanical alloying (MA) and spark plasma sintering (SPS). Effects of milling time as well as boron addition on the crystallite size, lattice strain, and powder morphologies of synthesized powders were studied using scanning electron microscope (SEM) and X-ray diffractometer (XRD). Synthesized powders were consolidated under uniaxial compression 50 MPa at 950 °C for 10 min. Shear punch and hardness tests were used to evaluate mechanical properties of consolidated specimens. Results show that Ni₃Al compound were synthesized after 30 h of milling in a planetary ball mill with the rotation speed of 350 rpm and ball-to-powder ratio 10:1. Synthesized powders have crystallite size in the range 15–20 nm depending on the milling time. Results also show that boron addition is influential the most when boron content is between 0.5–1.0 at%. Boron addition is accompanied with a significant improvement of hardness and shear strength and a drop in the ductility of Ni₃Al-xB (0.0<x<1.5 at%) alloy. The details concerning structure-properties relationship in this system are discussed in this paper. ...