H. Omar

Boron-aluminide coatings applied by pack cementation method on low-alloy steels

Abstract A simultaneous one-step boroaluminizing process has been performed on a 2.25Cr–Mo steel by means of pack cementation method using a B/Al boriding powder. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al and Fe and an inner layer containing mostly B and Fe. The layers were characterized by means of optical and scanning electron microscopy (SEM) in terms of coatings morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coating due to the boroaluminizing process.

Boro-nitriding of steel US 37-1

In this paper, we present a novel duplex surface treatment carried out on steel US 37-1. The as-produced multi-layer coating was characterised by optical microscopy, SEM, EDX and X-ray diffraction (XRD) and exhibited excellent adherence and morphology. The resulting layers were mainly borides, nitrides and boronitrides.

Boro-aluminising of P91 steel by pack cementation for protection against steam oxidation

Abstract High performance alloys are often the materials used for various components exposed to high temperature environments. In many cases, protective coatings are applied in these alloys, providing higher corrosion and oxidation resistance, compared to the base material. This study investigates the feasibility to apply boro-aluminising treatment on P91 steel by pack cementation process, to increase the steel high temperature properties in oxidising and corrosive environments. Packs activated by AlCl3, NH4Cl and KBF4 were used to carry out the coating deposition at a temperature of 715°C for 6 h. The coating formed was analysed by means of SEM and XRD, and the compounds formed were identified. Cyclic steam oxidation for a total of 1008 h at 650°C revealed an oxide scale of 50 μm for the uncoated P91 steel, while the coated steel shows practically no oxidation effect.

Fabrication of Open‐Cell Al Foams and Evaluation of their Mechanical Response under Tension

In the present paper a novel procedure for describing the solid geometry of open cell foams is introduced, facilitating the establishment of a corresponding FEM model for simulating the material behaviour in micro‐tension. Open‐cell Al‐foams were fabricated using the polymer impregnating method. A serial sectioning image‐based process is described to capture, reproduce and visualize the exact three‐dimensional (3D) microstructure of the examined foam. The generated 3D geometry of the Al‐foam, derived from the synthesis of digital cross sectional images of the foam, was appropriately adjusted to build a FE model simulating the deformation conditions of the Al‐foam under micro‐tension loads. The obtained results enabled the visualisation of the stress fields in the Al‐foam, allowing for a full investigation of its mechanical behaviour.

Surface Modification of Nickel Foams by a Slurry Aluminizing Process

A novel slurry‐based process for aluminizing nickel foams while improving the mechanical properties and conserving the excellent ductility is reported. Cellular unalloyed nickel foams with 92% porosity and uniform pore size and distribution were used as a starting material. Several slurries of different compositions were examined to investigate the possibility of developing an aluminide‐nickel intermetallic coating on a Ni foam without considerably degrading the original ductile properties of the foam. The process temperature was varying from 400 to 850° C and the process holding time was ranging between 2h to 6h. Scanning electron microscopy with an energy dispersive X‐ray spectrometry and X‐Ray diffraction were applied to assess the effectiveness of the aluminizing process and determine both the optimum parameters of the procedure (slurry composition, holding temperature and time) and the concentration profiles across the coating cross‐section. The mechanical behavior of the aluminized Ni‐foams was eval...

Determination of Mechanical and Corrosion Properties of Boride Coating on P91 Steel

In many applications, even high-performance alloys have to be covered with protective coatings, providing higher corrosion and oxidation resistance, as compared to the alloy itself. This study investigates the feasibility to apply boron coatings on P91 steel by pack cementation process, to increase the steel durability in oxidative and corrosive environments, as well as its mechanical strength. Micro-indentation and the coating impact test were used to characterize the hardness and fatigue properties of the film respectively. The coating corrosion resistance versus the one of the uncoated P91 steel was tested in a salt spray chamber. The coating performance was characterized by optical and scanning electron microscopy to check the consistency of the coated and uncoated surfaces and the oxidation extend. The results show an increased film strength, good fatigue performance and adequate corrosion resistance.