70    International Journal of Research in Advanced Engineering and Technology Online ISSN: 2455-0876 www.engineersjournals.com Volume 1; Issue 2; November 2015; Page No. 70-75 Effect of niobium addition on the structure and mechanical properties of aluminum bronze (Cu-10%Al) alloy Nwaeju C. C., Odo J. U., Nnuka E. E. Department of Metallurgical & Materials Engineering, Nnamdi Azikiwe University, Awka. Abstract This paper investigated the effect of niobium on the structure and mechanical properties of aluminium bronze. The properties studied were ductility, tensile and yield strengths, using universal testing machine model 50kN, impact strength using charpy machine model IT-30 and Brinell tester model B 3000 (H). The specimens were prepared by doping 1- 10% niobium into aluminium into the aluminium bronze (Cu-10% Al) at interval of one percent. The specimens were prepared according to BS 131- 240 standards. Microstructural analysis was conducted using L2003A reflected light metallurgical microscope. Results obtained shows that tensile strength, yield strength, impact strength and ductility increased by 10% respectively. 1% niobium shows increased in hardness result. Microstructural analysis revealed the primary α-phase, -phase (intermetallic phases) and fine stable reinforcing kappa phase and these phases resulted to the enhanced mechanical properties. Aluminium bronze doped with niobium proved to increased strength, ductility, and impact strength and reduces hardness and is therefore recommended for applications in engineering and allied industry. Keywords: microstructure, Niobium additives, Structure, Aluminium bronze. 1. Introduction Aluminium bronze is a type of bronze in which aluminium is the main alloying element added to copper. It is useful in a great number of engineering structures with a variety of the alloys finding applications in different industries [1] . According to ISO 428 specification [2] , most categories of aluminium bronze contain 4-10% wt % aluminium in addition to other alloying elements such as iron, nickel, manganese and silicon in varying proportions. The relatively higher strength of aluminium bronze compared with other copper alloys makes it more suitable for the production of forgings, plates, sheets, extruded rods and sections [3, 8] . Aluminium bronze gives a combination of chemo-mechanical properties which supersedes many other alloy series, making them preferred, particularly for critical applications [4] . Aluminium increases the mechanical properties of copper by establishing a face- centred-cubic (FCC) phase which also improves the casting and hot working properties of the base metal [5] . Other alloying elements example magnesium, iron, tantalum, etc. also improve the mechanical properties and modify the microstructure. Nickel and manganese improve corrosion resistance, whereas iron is a grain refiner [6] . Despite these desirable characteristics, most aluminium bronze exhibit deficient response in certain critical applications such as sub-sea weapons ejection system, aircraft landing gears components and power plant facilities. The need to overcome these obvious performance limitations in aluminium bronze is imperative to meet today’s emerging technologies. Structure modification in aluminium bronze is accomplished through any or combination of the following processes; heat treatment, alloying and deformation. The choice of method however is usually determined by cost, and effectiveness. The mechanical properties of aluminium bronzes depend on the extent to which aluminium and other alloying elements modify the structure. Niobium and its alloy exhibit properties that provided unique technological capabilities among refractory metals. It can be used as a hardening element in cast version and also it improves weldability of cast alloys [9] . This research work aims at modifying the structure of Cu-10% Al alloy, by using niobium and by impacting on the types, forms and distribution of phases within the matrix, and their effects on the mechanical properties. 2. Materials and Method 2.1 Materials and equipment The under listed materials and equipment were used for the research work: Pure copper scraps, pure aluminium scraps, niobium metal powder, weighing balance, crucible furnace, venire calliper, bench vice, lath machine, electric grinding machine, hack-saw, stainless steel crucible pot, mixer, scoping spoon, electric blower, rammer, moulding box, impact testing machine, hardness testing machine, universal tensile testing machine, metallurgical microscope with attended camera, etc. 2.2 Method a) Melting and casting of alloys: This operation was carried out to produce eleven separate specimens for the research work. The crucible furnace was preheated for about 15 minutes. For the control specimen, 153.33g of Cu and 16.67g of Al were measured out. Copper was charged into the furnace pre- set at 1150 o C and heated till it melted. Aluminium was then added and allowed to dissolve in the molten copper for 5 minutes. The alloying element (niobium) was then introduced based on compositions after the control sample had been cast.