MSE 250 – Chan Spring 2016
Homework #9 Due Tues., April 19, 2016
Show all work. Box final answers. 1. [4 points] Use the figures below for a Cu-Ni alloy to answer the following questions. (a) What is the electrical conductivity for a Cu-Ni alloy that has a yield strength of 125 MPa? (b) Is it possible to have a Cu-Ni alloy with minimum tensile strength of 375 MPa and also an electrical conductivity of 2.5 x 106 S/m? If not, why? If so, what wt% of Ni is required? 2. [5 points] A cylindrical wire with diameter of 2 mm is required to carry a current of 10 A with a minimum of 0.03 V per foot of wire. Using Table 18.1, Table 18.4, and the equations from slide 2 from Lecture 17, which material(s) would you choose for the wire? Show the calculations verifying that your material(s) of choice have suitable conductivities to meet the requirement.
[over, more problems on back]
3. [10 points] You are designing an underwater robot to search for sunken treasure in the ocean. You are considering the following alloys to use for the rivets and plates. For each alloy pair, answer the following questions (Lecture 19, Callister 17.2): (i) Will corrosion happen? Why? (ii) If corrosion does happen, which material should be the rivet and why?
(a) Aluminum alloy and magnesium alloy (b) Zinc alloy and low-carbon steel (c) Brass (60 wt% Cu – 40wt% Zn) and Monel (70 wt% Ni – 30 wt% Cu) (d) Titanium alloy and stainless steel 304 alloy (active) (e) Cast iron and stainless steel 316 alloy (passive)
4. [2 points] Iron Man’s suit is typically made entirely from a Au-Ti alloy. Due to budget cuts and the fact that Iron Man is always getting his suit scratched up during fights, the management in charge is considering making the suits out of Fe and only coating the surface with Au-Ti alloy. From a corrosion-resistance standpoint, do you agree or disagree with this decision, and why?