Effect Of Amorphous Layer On The Microstructure And Properties Of Al-B₄C Layered Composite

Aluminum metal matrix composites?Al-MMC also called AMC?consists of at least one metal and a reinforcement material,such as fiber,particles,compounds,oxides,carbide etc.,in order to achieve requirements and expected properties,which cannot be met by single compound materials.Though designing optimized structure,AMC can archive better performance.For example,mixing Al-alloy and B₄C powers together can archive a light and hard composite.Boron carbide?B₄C?has a high melting point,outstanding hardness,good mechanical properties,low specific weight,and great resistance to chemicals.Otherwise,Al alloys have low-density,low cost,and good properties.The composite material,also called a composition material or shortened to composite,is a material made from two or more constituent materials with significantly different physical and chemical properties that,when combined,produce a new material with characteristics different from each individual material.The individual components remain separate and distinct in a macro-scale structure.The material more abundant in one composite is called matrix and the other or others constituents are called reinforcements.The new composite material is be preferred for many reasons,because it is stronger,lighter,less expensive that,characters very appreciable in metal-mechanics industry.A three-layered?soft-hard-soft?composite proposed to take full advantage of,pure Al high ductility in the out-layers and a very hard B₄C-reinforcement in an Al-matrix as core?inner layer?.Such composite can combine the core high hardness and chemical stability of B₄C particle-reinforced and the outer layer weldability and toughness.Composites with big and hard reinforcements are desired to shielding and protective amour applications,also has applications as abrasive material and proton absorption.However,the addition of big particles of B4C also introduces some defects,such as brittleness elevation,high-unbound ratio and big properties gradient on reinforcement-matrix interface,being the interface line formation.In addition,the recommended balance of the ceramic reinforcements in AMCs is less than 20 wt.%,when this value is exceeded the AMC significantly increases their brittleness,but reducing the reinforcement content it reduces the hardness range and no longer meeting the high hardness requirements.In general,many routes can produce AMC;one of those is the powder metallurgy?PM?by blending elemental or pre-alloyed powders together.However,it is uneconomical to industrial production and the products of metallurgy can have limited shapes and feature.This limits its wide application.The casting method can achieve efficient production and low cost.However,some problems as particle agglomeration and low interface interaction between B₄C and Al need to be resolved.For reinforcements with big size,it is surface have many flaws that,when the composite are made reduces a lot the interface interactions and add many reinforcements defects as cracks due to previously cracks or sharps,interface line due to high roughness and void due to cracked reinforcements separation under stresses.In the present work,one solution for those big size reinforcements and wt.%is investigated,by means of;metal addition to promote diffusion from the grain though the matrix.Oxidation to remove the surface main flaws and surface acid attack?SAA?to remove the oxide layer reveal a regular and bounds disordered surface.In the end,a micro-amorphous transition?MAT?layer was made bounding the surface of the big-size B₄C?F60?in order to counter it or big size and high weight percentage disadvantages such as;High gradient properties between the hard reinforcement and ductile matrix leading the interface line and bad surface adhesion.Reinforcements surface defects and low Al-B₄C interface reactivity in normal conditions.Optimizing those parameters on the inner-layer,the final composite macro properties as hardness and toughness are also optimized allowing the utilization of high wt%.and reinforcement size in composites inner-layer.The result shows that,the composite inner-layer?Al-B₄C?shows a high macro-hardness of 43HBS1.5/125/30,once the out-layer pure Al has 16.5HBS1.5/125/30.However,due to the significant difference between Al and B₄C in the inner layer,there are always defects near their interface and exists a sharp hardness gradient.By means of surface alloying,oxidation and acid attack on the reinforcement surface,a micro-amorphous transition?MAT?layer is founded bounding the reinforcement's particles.This layer probably is constituted by Ni-Al,B-N intermetallic particles in an amorphous Al-Ni-B-C-O phase.The correct stoichiometry for this layer they microstructure are quite difficult to understand,once the traditional polishing process don't allow archive a flat surface,and the scanning microscopes as EPMA can't describe with high reliability good result in those conditions.The micro-hardness behavior shows the MAT-layer has⁹00 HV?1Kgf/30s?on the reinforcement boundary and decays exponentially until the transition layer have no effect on the Al-matrix?³2 HV?note that,Ni3Al a possible yielded intermetallic may be prominently increased through a strain hardening mechanism even up to 700 HV.This MAT layer bounding the reinforcement reduces the properties gradient and raises the composability,leading to a better impact resistance.