Characterization of hybrid joints formed by metallic inserts made of Ti alloys and polylactic acid (PLA) obtained by injection overmolding

• Grant number: 22/16254-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2023
• End date: December 31, 2023
• Field of knowledge: Engineering - Materials and Metallurgical Engineering
• Principal Investigator: Conrado Ramos Moreira Afonso
• Grantee: Carolina Neves Reis
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 18/18293-8 - Titanium alloys: phase transformations and additive manufacturing applied to obtaining functionally graded materials, AP.TEM

Abstract

In the present work, the study is focused on one of the types of dissimilar junctions known as Injection overmolding of Metal-Polymer hybrid structures. This technique is based on the traditional injection process used to form thermoplastic, thermosetting polymers and elastomers. The difference is the introduction of a metallic part inside the mold cavity (metallic insert), which presents a modified region responsible for mechanical adhesion with the polymer. That is, a surface area that has some initial roughness or is subjected to a surface modification so that there is penetration of the melted/plasticized polymer and, thus, mechanical locking after it solidifies. This roughness can be obtained by subtractive methods (erosion by blasting, removal by chemical attack, laser), by additive methods (oxide layers generated by electrochemical processing (MAO) or additive manufacturing - powder bed fusion) or by methods that do not remove and nor add material (pushing or chipping).The use of polymeric materials in the automotive, aeronautical, aerospace, naval and medical industries has been gaining interest in recent years since parts made from some thermoplastics, resins and composite materials with a polymeric matrix have low weight, good specific resistance (strength-to- weight ratio), high fracture resistance and recyclability (in the case of thermoplastics). Thus, the tendency is for polymer-metal hybrid structures to be produced more frequently in various industrial sectors, requiring the joining of dissimilar materials, which implies the search for joining techniques that present good mechanical response. There are already some combinations of metal alloys and polymers joined together through the Injection overmolding process. However, the joining of titanium alloys - Ti-6Al-4V (± + ²) and Ti-33Zr-33Nb (²) - with a biodegradable polymer is a relatively new topic.In this context, the objective of this work is to characterize dissimilar joints produced through Injection overmolding of Metal-Polymer hybrid structures between inserts made of two titanium alloys (Ti-6Al-4V and Ti-33Zr-33Nb), obtained through the conventional process of foundry, and biodegradable lactic acid polymer (PLA). In order to evaluate the feasibility of producing dissimilar parts by adapting the injection process and the properties of the joint obtained. The characterization techniques used will be optical microscopy (OM), scanning electron microscopy (SEM), Sonelastic ® impulse excitation technique, X-ray diffraction (XRD) for the metallic alloy, DSC thermal analysis for the polymer, Vickers in-line microhardness test along the interface or microhardness mapping, in order to provide an understanding of the transformations occurring in the polymer and at the interface of the welded dissimilar joint.